A revision of the genus Planinasus Cresson (Diptera, Periscelididae)

Abstract The genus Planinasus Cresson is revised and includes 18 extant and one fossil species. We clarify the status of the three previously described species and describe 15 new species as follows (type locality in parenthesis): Planinasus aenigmaticus (Colombia. Bogota: Bogota (04°35.8'N, 74°08.8'W)), Planinasus neotropicus (Panama. Canal Zone: Barro Colorado Island (09°09.1'N, 79°50.8'W)), Planinasus kotrbae (Ecuador. Orellana: Rio Tiputini Biodiversity Station (0°38.2'S, 76°08.9'W)), Planinasus miradorus (Brazil. Maranhão: Parque Estadual Mirador, Base da Geraldina (06°22.2'S, 44°21.8'W)), Planinasus tobagoensis (Trinidad and Tobago. Tobago. St. John: Parlatuvier (11°17.9'N, 60°39'W)), Planinasus xanthops (Ecuador. Orellana: Rio Tiputini Biodiversity Station (0°38.2'S, 76°8.9'W)), Planinasus argentifacies (Peru. Madre de Dios: Río Manu, Pakitza (11°56.6'S, 71°16.9'W; 250 m)), Planinasus insulanus (Dominican Republic. La Vega: near Jarabacoa, Salto Guasara (19°04.4'N, 70°42.1'W, 680 m)), Planinasus nigritarsus (Guyana. Conservation of Ecological Interactions and Biotic Associations (CEIBA; ca. 40 km S Georgetown; 06°29.9'N, 58°13.1'W)), Planinasus atriclypeus (Brazil. Rio de Janeiro: Rio de Janeiro, Floresta da Tijuca (22°57.6'S, 43°16.4'W)), Planinasus atrifrons (Bolivia. Santa Cruz: Ichilo, Buena Vista (4-6 km SSE; Hotel Flora y Fauna; 17°29.95'S, 63°33.15'W; 4-500 m)), P. flavicoxalis (West Indies. Dominica. St. David: 1.6 km N of junction of roads to Rosalie and Castle Bruce (15°23.8'N, 61°18.6'W)), Planinasus mcalpineorum (Mexico. Chiapas: Cacahoatan (7 km N; 15°04.1'N, 92°07.4'W)), Planinasus nigrifacies (Brazil. São Paulo: Mogi das Cruzes, Serra do Itapeti (23°31.5'S, 46°11.2'W)), Planinasus obscuripennis (Peru. Madre de Dios: Río Manu, Erika (near Salvación; 12°50.7'S, 71°23.3'W; 550 m)). In addition to external characters, we also describe and illustrate structures of the male terminalia and for Planinasus kotrbae sp. n., the internal female reproductive organs. Detailed locality data and distribution maps for all species are provided. For perspective and to facilitate genus-group and species-group recognition, the family Periscelididae and subfamily Stenomicrinae are diagnosed and for the latter, a key to included genera is provided.


Introduction
Flies of the genus Planinasus Cresson are uncommon in most collections and perhaps in nature. Their scarcity, coupled with their unusually wide heads (hypercephaly) -a feature that is more pronounced in males of some species--makes them even more of a curiosity and inviting subjects for study. As would be expected for a group that is not typically well represented in collections, the species are poorly known, and thus far, only three extant species and one fossil have been described (Prado 1975, Grimaldi and Mathis 1993.
Planinasus is known only from the New World tropics, and recent collecting there, especially in Bolivia, Brazil, Ecuador, Guyana, Mexico, Peru, and on islands of the Caribbean, has resulted in discovery of several additional species, all undescribed. Description of these species within the context of a species revision is the purpose of this paper.
The phylogenetic position of Planinasus relative to other Diptera has been confused, and while these relationships are somewhat clearer now (Winkler et al. 2010, Mathis and, definitive resolution continues to elude us. Cresson (1914) described Planinasus in the family Ephydridae, although he later suggested (1918) that the genus was probably not an ephydrid. Malloch (1934) first recognized Planinasus as a genus in the family Periscelididae, but that precedent was not accepted by all his successors. Curran (1934), for example, placed the genus in the family Drosophilidae, and Hennig (1969) preferred the family Aulacigastridae. More recently, McAlpine (1983) again assigned the genus to Periscelididae, and we also subscribe to that precedent Mathis 1994, Mathis and with qualification and herein present additional evidence and discussion that explains that phylogenetic placement.
The nomenclatural history of the genus and its included species is uncomplicated, as would be expected for a little-known genus that comprises few species. When Cresson (1914) first proposed the genus, it was monotypic, with P. ambiguus Cresson as its type species. Malloch (1934) described a second genus, Schizochaeta, which was also monotypic, being based on S. shannoni, a new species that Malloch described in the same paper. Hennig (1969), who reviewed the group, suggested that P. ambiguus and S. shannoni were congeneric, synonymized Schizochaeta with Planinasus, and described a third species, P. venezuelensis. Grimaldi and Mathis (1993) described the fourth species, P. electrus, which is a fossil preserved in Dominican Amber. Except for McAlp-ine's (1978McAlp-ine's ( , 1983, Winkler et al. (2010) and Mathis and Rung's (2011) discussion of placement of Planinasus in the family Periscelididae and phylogenetic relationships, the genus has not been treated substantively by others.

Methods and materials
Most of the species considered herein are newly described, and in their individual treatments, we have included all specimens that were available and that could be reliably identified. Specimens included in type series are more restricted, particularly those for which identifications are based primarily on characters of the male terminalia. Other specimens are listed with the appropriate species under the section "Other specimens examined." Type specimens of all nominate taxa were studied. Label data accompanying each holotype are quoted verbatim with a slash mark to separate data of one label from another. Clarifying or interpretive comments are included within brackets.
Descriptions of species are composite if specimens other than the holotype were available. For the most part, information given in the generic description is not repeated in the species descriptions. The descriptive terminology follows that published in the recent Manual of Nearctic Diptera (McAlpine 1981) with the modification noted below. We follow Sabrosky (1983) in using the term "microtomentum" rather than pruinosity. We use the term basal flagellomere for the large antennomere beyond the pedicel. We prefer this term over "first flagellomere" as there may be more than one flagellomere involved, and basal does not imply a number or numbers. We likewise do not use "postpedicel" (Stuckenberg 1999) for this antennomere because at least the multisegmented arista is beyond the pedicel in addition to the large antennomere, and postpedicel is thus ambiguous and lacking in precision.
We have adopted the nomenclature of Cumming et al. (1995) for describing structures of the male terminalia with the following exception: we use the term pregonite with reference to the basal plate closely associated with the arms of the hypandrium and the bacilliform sclerites; and the term postgonite with reference to the complex clasper-like structure closely associated with the phallapodeme basally, the phallus medially, and the pregonites laterally. The usage of these terms follows Griffiths (1972) in that they are provisional and do not indicate any firm opinion on homology. One of these structures, probably the postgonite, seems to correspond to the "gonostyles" of Cumming et al. (1995). We described the diagnostic features of the male terminalia from three views: lateral view of the epandrium (including the hypandrium when attached); ventral view of the epandrium and internal structures; and lateral view of the internal structures. We also provide an illustration and description of the ejaculatory apodeme. When the epandrium and associated structures were illustrated in ventral view, some parts of the image, including the epandrium, were not done in the same exact position, and to avoid ambiguities of interpretation that could arise when observing structures from this view, we concentrate on the shape of the hypandrium, pregonite and lobe and setae of the postgonite.
Because specimens are small, usually less than 3.50 mm in length, study and illustration of structures of the male terminalia and female reproductive organs required use of a compound microscope. Observation of detailed structures of the male terminalia was sometimes needed to confirm a species' identification.
Dissections of male terminalia were performed following Clausen and Cook (1971) and Grimaldi (1987). Abdomens were removed with microforceps and macerated in a sodium hydroxide solution. Cleared genitalia were then transferred to glycerin for observation. The dissected abdomen was placed in a plastic microvial filled with glycerin and attached to the pin supporting the remainder of the insect from which it was removed. The female reproductive organs were dissected from freshly collected specimens and embedded directly in polyvinyllactophenol with an admixture of chlorazol black E, which stains the unsclerotized cuticle blue.
Distribution maps were made using ESRI ArcView7 GIS 3.2. Longitude and latitude coordinates were obtained for the locality where each specimen was collected and entered into a Microsoft Excel © spreadsheet. If unavailable directly from specimen labels, longitude and latitude were estimated using gazetteers and maps, usually available electronically, to determine the geographical coordinates.
Three head ratios are used commonly in the descriptions and are defined here for the convenience of the user (ratios are averages of three specimens).
1. Head ratio: head height (distance from peristomal margin to vertex)/head width. The measurements were taken from the head from an anterior view.
2. Facial ratio: interantennal width (shortest distance between antennal bases)/ facial height (distance in the middle of the face between the ptilinal suture and the ventralmost margin of the face). The measurements were taken from the head from an anterior view.
3. Frontal ratio: frontal width (straight line distance between compound eyes at the level of the anterior ocellus)/frontal height (distance between the ptilinal suture (anterior margin of the frons) and the vertex. The measurements were taken from the head with an orientation to make the frons flat in the field of view.
The author's contributions generally adhered to the following division of labor: most of the descriptive work was done by the first two authors, and the species names are attributed to them; the third author contributed information on the female reproductive system and observations on mating behavior. All three participated in field work together in Ecuador, where many of the specimens were collected and where observations and preliminary dissections were made.
Although this study was based primarily on specimens in the National Museum of Natural History, Smithsonian Institution (USNM), numerous others were borrowed, particularly primary type specimens of the species described previously. To our colleagues and their institutions listed below who lent specimens, we express our sincere thanks. Without their cooperation this study could not have been completed. and Rung 2004) and the small Neotropical genus Somatia Schiner (tentatively in a separate subfamily, the Somatiinae) to belong in the Periscelididae. Although Mathis and Papp (1992) and Grimaldi and Mathis (1993) questioned the placement of Diopsosoma in the Periscelididae, Mathis and Rung (2004) presented five synapomorphies that confirm its inclusion. Mathis (1993) considered Somatia as closely related to the Psilidae (Diopsoinea), while D. K. McAlpine (1997) treated Somatiidae (monotypic) as incertae sedis. Diagnosis. Head: Frons with 2 fronto-orbital setae, 1 reclinate, usually 1 proclinate; at least 1 vertical seta (apparently the lateral) present; postvertical setae usually lacking (present in some Stenomicra, where they are slightly divergent); ocellar setae lacking (a synapomorphy, although present in fossil Procyamops). Pedicel bearing 1 or more dorsoapical setae. Thorax: Postpronotum frequently polished, lacking a well-developed seta (a synapomorphy). Wing: No costal breaks, although with weak areas; C extended to vein M; cell cup present, CuA 2 usually well developed (weakly developed or lacking in Stenomicra).
The subfamily Stenomicrinae was first proposed as a monogeneric family with Stenomicra Coquillett as its type genus (Papp 1984). As we accept McAlpine's proposal that Stenomicra is related to Planinasus and Cyamops and that this assemblage of genera and those of the subfamily Periscelidinae are likewise related, we prefer recognition of an expanded concept of Periscelididae, with Periscelidinae and Stenomicrinae as included subfamilies.
Distribution. Known only from the New World tropics. Natural History. Specimens of Planinasus are generally rare in collections, and nothing is known about their immature stages, life cycle, or ecology. Their rarity in collections, however, is not necessarily a reflection of their diversity and/or abundance in nature. Specimens are comparatively small, obscure, and could easily be overlooked. We have collected hundreds of specimens of numerous species in the countries of Bolivia, Ecuador , Guyana, Mexico (Chiapas), Peru (Huánuco, Cuzco, Madre de Dios), and on some islands of the Caribbean (Cuba, Dominica, Dominican Republic, Jamaica, and Tobago). In all areas, specimens were collected by sweeping dense, understory vegetation--some bearing flowers--that was associated with shaded, damp, habitats. In Ecuador, we found specimens to be relatively common on the exposed sand or mud substrates in shaded, riparian habitats. Here we observed specimens exposed on the surface of stones or large fallen leaves, perhaps posturing to be seen by conspecifics. We captured numerous specimens alive by simply and carefully lowering a vial over them.
Our field work and sampling, regardless of the collecting technique, also indicates that two to four species frequently occur sympatrically at the same microhabitat. We observed that one species at these sites usually predominates in numbers of individuals. How the various species partition the habitat and what their population structure is are basic questions that remain unanswered. Grimaldi and Fenster (1989) noted certain preconditions associated with male hypercephaly. Although their list primarily pertains to Drosophilidae, they may also apply elsewhere in Diptera, including species of Planinasus that demonstrate hypercephaly. These preconditions, which were manifested at least partially in the few observations we made (see "Mating behavior" under P. kotrbae), are: territoriality, faceto-face confrontations, head butting and jousting. Perhaps, like Drosophilidae, there is more aggressiveness among species with hypercephaly than their unmodified relatives. Further observation and comparison are obviously needed, and we hope that this revision will foster such.
Discussion. Several species exhibit considerable sexual dimorphism, especially in the width and coloration of the face. Males in these species tend to have wider faces (hypercephaly), i.e., larger facial ratios, and frequently there is a distinctive colorational pattern. The facial pattern usually also involves microtomentum or its absence in additional to color. These details are included in descriptions of appropriate species.
Within the subfamily Stenomicrinae the sister group of Planinasus is apparently either Cyamops or Stenomicra (Winkler et al. 2010, Mathis and or perhaps both. The relationship with Cyamops is based on the following putative synapomorphies: 1. Midtibia with an apical, anteroventral spine-like seta. 2. Arista bipectinate (McAlpine 1983: 56). 3. Face bearing a dorsoclinate pair of setae, these usually inserted above other facial setae.
Planinasus is distinct from other genera of Periscelididae and its monophyly is established by the following putative synapomorphies: 1. Frons bearing a pair of interfrontal setae that are usually slightly reclinate to dorsoclinate. The interfrontal setae, as described, are unique to Planinasus.
6. Hindfemur with a subapical dorsal seta. 7. Anepisternum with 1-2 setae along posterior margin (relatively common in other taxa of Asteioinea Diagnosis. This species group is distinguished by the following combination of characters: Head: Interfrontal seta short, about half length of lateral vertical seta. Antennal coloration variable; pedicel with short ventral projection; basal flagellomere short, about as high as long. Large facial setae arranged in 2-3 transverse rows; face of males and females similar in shape and color. Thorax: Anepisternum with 1 large seta along posterior margin. Wing hyaline to faintly infumate. Forefemur of male lacking subapical, irregular, pale-colored annulus, bearing 2 large seta at apical 1/3 along posteroventral surface. Abdomen: Surstylus generally thumb-like, without posterior processes or lobes, in nearly vertical alignment with anterior margin of epandrium; postgonite with robustly developed lobe bearing numerous setulae apically; phallus mostly sclerotized, large, convoluted; ejaculatory apodeme generally well developed, at least as long as phallapodeme, with expanded apex. Discussion. There is little if any dimensional or colorational sexual dimorphism in specimens of this species group. Dimensions and ratios of the heads of both males and females are essentially the same or with broad overlap. Species of this group share with species of the nigritarsus group, and only with them, a postgonite with a robustly developed lobe that bears numerous setulae. In other species of Planinasus, the lobe of the postgonite, which is generally less developed, bears fewer than four apical setulae, and fewer than six setulae overall. The ambiguus and nigritarsus groups also share a well-developed ejaculatory apodeme that is at least as long as the phallapodeme (this character state is also present in P. mcalpineorum sp. n. of the nigrifacies group).
Remarks. This species, represented by two males only, is known only from Colombia and is the only species of Planinasus known to occur in that country. It is very similar to P. neotropicus and P. ambiguous, and analysis of the male genitalia is generally necessary to distinguish among the three species. Characters of the male terminalia of P. ambiguous are very distinct, particularly the shape of the epandrium (Fig. 10), the length and shape of the surstylus (Fig. 9), and the uniform, U-shaped hypandrium. From P. neotropicus, P. aenigmaticus can be easily distinguished by the surstylus, digitiform over its entire length and with about four posteromedial setulae (Fig. 1), and the U-shaped hypandrium with the anterior margin bearing a short, trapezoidal projection (Fig. 2). In P. neotropicus, the surstylus is bulged basally, there is only one medial seta on it (Fig. 15), and the hypandrium is V-shaped (Fig. 16).
Type material.   Remarks. This widespread species was previously known only from Costa Rica and Peru (Hennig 1969) and is here recorded from as far north as Chiapas, Mexico, and to the south as far as Peru (Madre de Dios). This species can be easily confounded with the other two species in the ambiguus group based on external characters, but characters of the male terminalia of P. ambiguus unambiguously diagnose this species. See "Remarks" under P. aenigmaticus sp. n. for further discussion.
Etymology. The species epithet, neotropicus, is to recognize the Neotropical distribution of this species and is a noun in apposition.
Remarks. This species, like P. ambiguus, is relatively widespread, especially in Andean countries. It can be easily confounded with the other two species in the ambiguus group based on external characters. See "Remarks" under P. aenigmaticus sp. n. for further discussion on how to distinguish among P. aenigmaticus sp. n., P. ambiguus and P. neotropicus sp. n.
Diagnosis. This species group is distinguished by the following combination of characters: Head: Interfrontal seta long, subequal to length of lateral vertical seta. Antennal coloration variable; pedicel with elongate ventral projection; basal flagellomere long, length nearly twice height. Large facial setae arranged in 2-3 transverse rows; face of females bulbous, evenly transversely arched, mostly black. Thorax: Anepisternum with 2-4 weak setae along posterior margin. Wing strongly infumate. Forefemur of male lacking a preapical yellowish annulus, bearing 1 large, posteroventral seta at apical 1/3. Abdomen: Surstylus generally without posterior processes or lobes (P. kotrbae has a process), in nearly oblique alignment with anterior margin of epandrium (except in P. tobagoensis); postgonite with small, finger-like lobe bearing a few apical setulae; phallus mostly membranous (more heavily sclerotized in P. shannoni); ejaculatory apodeme generally reduced, inconspicuous in some species.
Discussion. The species of this group demonstrate considerable sexual dimorphism. The dimorphism is most evident in the shape and coloration of the face. The shape and coloration of the male face varies, depending on the species, but the face of females is quite similar in three species and is generally dark colored and conspicuously projected forward, bulbous, evenly arched transversely, somewhat flat in lateral view on ventral half. Species of this group share, with species of the atriclypeus group and with P. obscuripennis sp. n. (the obscuripennis group) the reduced number of setae on the postgonite (2-6), and the ejaculatory apodeme is generally reduced or inconspicuous. In other species of Planinasus, the lobe of the postgonite, which is generally better developed, bears more than 20 setulae, and the ejaculatory apodeme is large, with a fan-like apical expansion.
Head: Frons mostly bare of microtomentum, shiny, except for densely microtomentose, velvety-appearing, anterolateral corners, blackish brown; frons much wider than long, frontal ratio averaging 0.48; interfrontal seta long, length subequal to that of lateral vertical seta. Antenna generally blackish brown, basal flagellomere partially yellowish basally; pedicel with ventral projection long, about 1/2 length of basal flagellomere; basal flagellomere long, slightly more than twice basal width; arista bearing 13-14 dorsal rays, 3-4 ventral rays. Face very wide, facial ratio averaging 0.96; face mostly black, black coloration extended to ventral margin of face, lateral margin just ventrad of antennal groove whitish yellow, concolorous with coloration of adjacent parafacial; facial microtomentum sparse or lacking, mostly shiny; midfacies with a conical prominence, shaped like an inverted V; antennal grooves shiny, lacking narrowly triangular, bare area extended medioventrally from ventral margin of antennal groove to oral margin; large facial setae 4-5, not arranged in transverse rows, becoming smaller ventrally; largest seta inserted dorsolaterally, dorsoclinate and slightly convergent; 2nd largest seta inserted medioventrally from largest seta, porrect and parallel; sometimes with a smaller seta inserted just above porrect seta; 2 setae inserted at margin of black and yellowish white color, these oriented ventrally. Clypeus and palpus blackish brown. Gena concolorous with lateral margin of face.
Description of female. Same as male except as follows: Head: Frontal ratio averaging 0.55; face and antenna mostly blackish brown, lateral margin of face (immediately adjacent to parafacial) whitish yellow; face not as wide, facial ratio averaging 0.42; face projected forward on ventral 1/2, bulbous, evenly arched transversely, shallowly arched vertically, mostly flat.
Abdomen: Internal female reproductive tract : Common oviduct opening anterodorsally into vagina. Posterior to this, paired spermathecae and accessory glands opening adjacent to each other into dorsal vaginal wall. Each spermatheca consisting of ovoid dark brown chamber with shallow circular depression apically; its sclerotized wall slightly wrinkled with tiny dimples; no basal introvert present. Spermathecal ducts lined by thick cuticle with more or less distinct annulation, sometimes slightly sclerotized at their base. Accessory glands about as long as spermathecae; their gland reservoirs and ducts lined by membranous cuticle. Ventral receptacle colourless, onechambered, arising from anteroventral portion of vagina, round with circular apical depression, thus resembling (an inverted toilet plunger or) a shallow double-walled bowl.
Type material.  [red]." The holotype is double mounted (minuten pin in plastic block), is in excellent condition, and is deposited at the USNM.   Etymology. The specific epithet, kotrbae, is Latin genitive patronym to honor Dr. Marion Kotrba (ZSMC), who conducted field work with us in Ecuador and allowed us to use her rearing cage for making observations on the mating behavior of this species. Marion directly participated in making these observations. Mating behavior. Marion Kotrba and W. N. Mathis observed the mating behavior of P. kotrbae in the field (Ecuador. Orellana: Rio Tiputini Biodiversity Station (0°38.2'S, 76°08.9'W)) and in a rearing cage in the laboratory. In the field, we observed what we called "head butting" on repeated occasions, especially on leaves laying on the substrate. This refers to the specific behavior of males confronting each other head on and then lunging forward, making physical contact with the front of the head. Marion collected several specimens that she released into a rearing cage. Within minutes the specimens were mating and going through sequences of mating behavior. We observed 10 matings with the following durations: 1×2s, 2×5s, 1×10s, 4×15s, 2×18s. It cannot be decided whether all of these were successful in terms of sperm transfer. Two behavioral elements commonly observed within the context of mating were "kissing" and an "arc dance". Between matings and also at other encounters the flies frequently made contact with the frontally extended proboscis. These "kisses" lasted up to about 4 seconds with sometimes only a brief second between. "Kissing" was observed a few times between specimens of the same gender. When "arc dancing" a male would shuttle back and forth laterally with spread wings while facing the female at a short distance of only a few centimeters. The lateral movements were usually in a short arc pattern of 30-45° but up to 180°. One observed mating sequence consisted of five matings, 24 kisses and four arc dances in total. Another male demonstrated no lateral movements after mating and kissing a female just once.
Having access to a rearing cage facilitated observations in the laboratory as well as temporarily holding specimens that were to be dissected. Keeping females to be dissected in the cage ensured their freshness, which makes dissecting easier, and the preparations that resulted were excellent. The tissue is pliable and extraneous material, such as tracheoles, can easily be removed.
Remarks. This species is a member of the shannoni group and is distinguished from other congeners of that group by the black antenna in both sexes, the mostly shiny black face except for the whitish yellow, lateral margin immediately adjacent to the parafacial, the conically prominent face of the male, and the mostly yellowish femora (only the apices are dark colored). The presence of a basal projection on the surstylus also distinguishes this species from other members of the same species group.
Thorax: Forefemur lacking preapical annulus. Distribution (Fig. 34). Neotropical: Brazil (Maranhão). Etymology. The specific epithet, miradorus, is to recognize the name of the state park in the Brazilian state of Maranhão where the type locality is located and is a noun in apposition.
Remarks. This species is very similar to P. shannoni and especially to P. venezuelensis but can be distinguished from these and other congeners of the shannoni group by the distinctively colored male basal flagellomere, which is markedly twotoned with the base whitish yellow and the apical half black. The surstylus is very similar in shape to that of P. venezuelensis, but other characters of the male terminalia, such as the relatively well-developed ejaculatory apodeme, the outspread arms of the postgonite in ventral view, and the general shape of the postgonite in lateral view distinguish this species from P. venezuelensis. Furthermore, colorational characters of the basal flagellomere are very distinctive and constant in the sampling available to us, and based on this evidence, we are currently of the opinion that this is a separate species. Species of the shannoni group, this species and P. venezuelensis in particular, would be excellent candidates for molecular analysis to test the strength of the morphological characters. Head: Frons mostly bare of microtomentum, shiny, except for densely microtomentose, velvety-appearing, anterolateral angles, blackish brown; frons much wider than long, frontal ratio averaging 0.42; interfrontal seta long, length subequal to that of lateral vertical seta. Scape and pedicel blackish brown except for whitish yellow, ventral projection of pedicel; pedicel with ventral projection long, about 1/2 length of basal flagellomere; basal flagellomere long, slightly more than twice basal width, yellowish; arista bearing 13-14 dorsal rays, 3-4 ventral rays. Face very wide (at least of male), facial ratio 0.67; dorsal 2/3 (above transverse carina) wide, shieldlike, medial portion (between antennal bases) moderately densely microtomentose, mostly whitish but with blackish brown background coloration also appearing, lateral portion (just below antennae) bare, shiny, especially ventrally, and with ventral margin of antennal grooves quite evident; ventral 1/3 of face (below transverse facial carina) mostly densely microtomentose, somewhat shiny, whitish to whitish yellow, with blackish, somewhat bare, narrowly triangular area extended obliquely medioventrally from ventral margin of antennal groove; large facial setae 3, not arranged in transverse rows, becoming smaller ventrally; largest facial seta inserted dorsolaterally, dorsoclinate and convergent; 2nd largest seta inserted medioventrally from largest seta, porrect and parallel; 3rd seta inserted ventrolaterally and with porrect to slightly ventroclinate orientation. Clypeus and palpus blackish brown. Gena concolorous with ventral 1/3 of face.
Description of female. Same as male except as follows: Head: Frontal ratio 0.55; face and antenna entirely blackish brown; face not as wide, facial ratio 0.32; face projected forward on ventral 1/2, bulbous, evenly arched transversely, shallowly arched vertically, mostly flat.
Thorax: Forefemur lacking preapical annulus. Type material. The holotype male is labeled "IquitosPeru MarApr1931 RCShannon/Type No. 49549 U.S.N.M. [red, number handwritten]/Schizochaeta shannoni Type det. JRMALLOCH [species name and "Type" handwritten, label has a black sub-border]." The holotype is double mounted (glued to a paper point), is in fair condition (the middle and hind right legs are missing), and is deposited in the USNM (49549). The allotype female and four additional paratypes, all males, bear the same locality, date, and collector data as the holotype. In the original description, Malloch stated that a paratype would be deposited in the British Museum (Natural History).
Etymology. Malloch named this species after his friend and fellow dipterist, Raymond Corbett Shannon, who was the collector of the type series. R. C. Shannon conducted much field work in the Neotropical Region and most of his collections were donated to the USNM.
Remarks. This species is very similar to P. venezuelensis but is distinguished from it by the mostly yellow mid-and hindfemora, which have at most the apical one-fourth to one-third dark, and the shape of the surstylus (Fig. 35) short and widely truncate apically. The surstylus of P. venezuelensis is long, J-shaped. From other congeners, this species is distinguished by the following characters of males: the pale-colored basal flagellomere and apex of the ventral projection of the pedicel, the whitish microtomentum on the mid-dorsal surface of the face, the relatively approximate antennal bases, and the narrowly triangular areas that extend medioventrally from the ventral margin of the antennal groove. The shape of structures of the male terminalia also clearly distinguishes this species (see Figs 35-38).
Etymology. The specific epithet, tobagoensis, is to recognize the island where the type locality is located.
Remarks. This species is known from northern South America, including Trinidad and Tobago. It keys out near P. kotrbae. Besides the characters given in the key, it can be easily distinguished from that species by the absence of a basal process on the surstylus and a roughly diamond-shaped pregonite (roughly triangular in P. kotrbae).

Description of male.
Moderately small to medium-sized flies, body length 2.35-3.10 mm.
Natural history. Adults of this species were fairly common on vegetation in the understory of gallery forests along the Rio Manu. The flies occurred on prominent, frequently sun-lit, broad leaves, especially in stream bottoms, where males displayed and courted females and drove off other males.
Remarks. This species is very similar to P. shannoni and P. miradorus but can be distinguished from these and other congeners of the shannoni group by the following characters of males: the pale-colored, unicolorous basal flagellomere and apex of the ventral projection of the pedicel, the whitish microtomentum on the mid-dorsal surface of the face, the relatively approximate antennal bases, and the narrowly triangular areas that extend medioventrally from the ventral margin of the antennal groove. Males and females are distinguished by the mostly black middle and hind femora (only the basal one-fourth to one-third yellowish in males, and for females only the basal oneeighth is yellowish). See "Remarks" under P. venezuelensis for further discussion of similarities and differences. 9. Planinasus xanthops sp. n. urn:lsid:zoobank.org:act:6C187AF2-BC7F-4BDC-BF53-E699ED5FE7A9 http://species-id.net/wiki/Planinasus_xanthops Figures 48-52 Description of male. Moderately small to medium-sized flies, body length 2.10-3.05 mm.
Distribution (Fig. 52). Neotropical: Ecuador (Orellana). Etymology. The specific epithet, xanthops, is of Greek derivation, meaning yellow face, and refers to yellow face and antennae of males.
Diagnosis. This species group is distinguished by the following combination of characters: Head: Interfrontal seta long, subequal to length of lateral vertical seta. Antenna yellow to yellowish orange with some blackish coloration dorsally; pedicel with short ventral projection; basal flagellomere long, length nearly twice height. Large facial setae arranged in a single transverse row of about 8 setae; face of females somewhat bulbous, evenly transversely arched, mostly black dorsally, densely silvery white, microtomentose ventrally. Thorax: Anepisternum with 3-4 small setae along posterior margin. Wing moderately to strongly infumate. Forefemur of male lacking a pale, irregular, subapical annulus, bearing 1 large, posteroventral seta at apical 1/3. Abdomen: Surstylus generally bearing a basal process and generally in nearly oblique alignment with epandrium; postgonite with robustly developed lobe bearing numerous setulae apically; phallus mostly sclerotized, convoluted; ejaculatory apodeme generally welldeveloped, at least as long as phallapodeme, with expanded apex.
Discussion. Species of this species group share, with species of the ambiguus group, and only with them, a postgonite with a robustly developed lobe that bears numerous setulae. In other species of Planinasus, the lobe of the postgonite, which is generally less well developed, bears fewer than four apical setulae, and fewer than six setulae overall. The nigritarsus and ambiguus groups also share an ejaculatory apodeme that is generally well developed, at least as long as the phallapodeme, but this character state is also present in P. mcalpineorum sp. n. (the nigrifacies group). The presence of a basal process on the surstylus that bears a setula distinguishes the nigritarsus group from most other groups of Planinasus, but it is also present in P. kotrbae.
Head: Head ratio 0.51-0.54; frons generally brownish black to black, mostly moderately microtomentose, dull to faintly subshiny, except for densely microtomentose, velvet-like, anterior margin, including area laterad of antennal bases; frons wider than long, frontal ratio 0.49-0.53; interfrontal seta shallowly curved, elongate, length subequal to length of lateral vertical seta. Antenna mostly yellowish orange, especially medially and ventrally; dorsum of pedicel and basal flagellomere brownish to blackish; basal flagellomere moderately long, length conspicuously greater than width at base, tapered to moderately acute point at apex, dorsal and ventral margins nearly straight, at most very shallowly curved; pedicel with ventral projection short, not extended anteriorly much beyond dorsal margin, bearing moderately long, ventroapical seta (not extended to apex of basal flagellomere); arista bearing 13-14 dorsal rays, 3-4 ventral rays. Face comparatively wide, facial ratio 0.58-0.62; dorsad of transverse carina moderately microtomentose, subshiny, mostly blackish brown, but becoming brownish to yellowish toward antennal grooves; ventrad of transverse carina densely microtomentose, carina and immediately ventrad blackish brown, thereafter ventrally densely silvery white to slightly yellowish along peristomal margin, sericeous; large facial setae arranged in a more-or-less single transverse row of about 8 setae, medial pair approximate, porrect to shallowly ventroclinate, next seta shallowly curved dorsally, lateral 2 setae ventroclinate. Clypeus and palpus brownish black; clypeus variable, all yellow, two-toned, to all black with some silvery white microtomentum.
Description of female. As in male except as follows: Head generally narrower, head ratio 0.65-0.67; frontal ratio 0.55-0.56; facial ratio 0.  [red]." The holotype is double mounted (minuten pin in a plastic block), is in excellent condition, and is held in trust at the USNM for eventual deposit in Peru.  Distribution (Fig. 57). Neotropical: Brazil (Amazonas), Ecuador (Orellana), Peru (Loreto, Madre de Dios), and Venezuela (Amazonas).
Etymology. The specific epithet, argentifacies, if of Latin derivation and refers to the distinctive, silvery microtomentum on the ventral one-third of the face.
Remarks. Structures of the male terminalia of this species and those of P. nigritarsus are very similar, and based on these morphological characters alone, we would have suggested that these two species are conspecific. There are external characters (see diagnosis and key) that clearly distinguish between these two species, however, and based on these, we conclude that they represent closely related but separate species. 11. Planinasus insulanus sp. n. urn:lsid:zoobank.org:act:1DB5CFBA-9C02-48DB-8C25-8112EFBBF539 http://species-id.net/wiki/Planinasus_insulanus Figures 58-64 Description of male. Small to moderately small flies, body length 1.60-2.80 mm.
Etymology. The species epithet, insulanus, is of Latin derivation, meaning island and refers to the occurrence of this species on West Indian islands.
Remarks. Variation in wing coloration is particularly evident in specimens of this species and may be related to the age of specimens, older specimens having darker wings, but also to underlying genetic variation. The shape of the surstylus and hypandrium readily distinguish this species from congeners. 12. Planinasus nigritarsus sp. n. urn:lsid:zoobank.org:act:BD9CEBD6-C6B1-492B-A19B-D4FC36C7595E http://species-id.net/wiki/Planinasus_nigritarsus Figures 65-69 Description of male. Moderately small flies, body length 2.10-2.80 mm.
Type material.  [red]". The holotype is double mounted (minuten in a block of plastic elastomere), is in excellent condition, and is held in trust at the USNM for eventual deposit in Guyana. Nineteen paratypes (13♂, 6♀; USNM) bear the same label data as the holotype. Other paratypes are as follows: Same locality as the holotype but with dates from 13 Apr-28 Aug 1994, 1997 (17♂, 5♀; USNM).
Remarks. See "Remarks" under P. argentifacies for a discussion on distinguishing characters as well as similar morphological characters.
Diagnosis. This species group is distinguished by the following combination of characters: Head: Interfrontal seta short, about half length of lateral vertical seta. Antennal coloration variable; pedicel with short ventral projection; basal flagellomere short, about as high as long. Large facial setae arranged in 2-3 transverse rows; face of males and females similar in shape and color. Thorax: Anepisternum with 1 large seta along posterior margin. Wing hyaline to faintly infumate. Forefemur lacking sub-apical, irregular, pale-colored annulus, bearing 2 large seta at apical 1/3 along posteroventral surface. Abdomen: Surstylus in nearly oblique alignment with epandrium, generally bearing a posterior process, or lobe, with a setula; postgonite generally with a digitiform lobe bearing a few setulae apically; phallus mostly membranous; ejaculatory apodeme generally greatly reduced.
Discussion. This species group may not be monophyletic, being based primarily on plesiomorphic characters, and comprises the "remainders" species that could not be conveniently placed in other groups. Species of this group share, with those of the shannoni group, and with P. obscuripennis the greatly reduced phallapodeme (conspicuous only in P. nigrifacies in this group) and the small number of setulae on the lobe of the postgonite (less than 6). Furthermore, in the shannoni and nigrifacies groups, the phallus is only partially sclerotized, contrasting with the heavily sclerotized phallus typical of species of the nigritarsus and ambiguus groups. Head: Head ratio 0.62-0.65; frons generally uniformly brownish black to black, mostly very finely and sparsely microtomentose, subshiny to shiny, except for more densely microtomentose, anterolateral angles and slightly undercut anterior margin; anterolateral angles setulose; frons wider than long, frontal ratio 0.53-0.57; interfrontal seta shallowly curved, moderately elongate, about 2/3 length of lateral vertical seta. Antenna mostly uniformly black; some specimens with ventral portion of basal flagellomere and pedicel faintly yellowish brown; basal flagellomere moderately short, length at most only slightly greater than height at base, tapered gradually to narrowly rounded acute, dorsal and ventral margins nearly straight;; pedicel with ventral projection short, length of projection conspicuously less than length of pedicel without considering projection, bearing long, ventroapical seta (extended slightly beyond apex of basal flagellomere), 1 dorsoapical seta, 1 dorsal seta; arista bearing 13-14 dorsal rays, 3-4 ventral rays. Face comparatively narrow, facial ratio 0.34-0.37; portion dorsad of transverse carina moderately large, sparsely microtomentose, subshiny to shiny, mostly brownish to bluish black; antennal grooves especially shiny; ventrad of transverse carina more densely microtomentose, yellowish brown medially, moderately sparsely silvery yellow microtomentose, sericeous, lateral portions of face becoming bluish black; large facial setae arranged in approximately 2 transverse rows; dorsal row with 6 setae, medial pair of dorsal row moderately widely separate, shallowly dorsoclinate; next setae much shorter, shallowly ventroclinate; ventral row with 6 setae, all ventroclinate, medial pair slightly shorter than others. Clypeus brownish black to black with very sparse whitish yellow microtomentum; palpus brownish black.
Description of female. As in male except as follows: Head generally slightly narrower, head ratio 0.65-68; frontal ratio 0.44-48; facial ratio 0.34-37. Face mostly uniformly bluish black, silvery white microtomentum more evident.
Remarks. This species is most similar to P. atrifrons. Besides the characters given in the key, it can be distinguished from that species by structures of the male terminalia, particularly the unevenly bilobed surstylus, with anterior lobe much larger, digitiform, rounded apically, and a short, shallowly pointed posterior lobe. In P. atrifrons, the surstylus is swollen medially, and the apex makes a nearly right angle with the main surstylar apex (Fig. 73).
Abdomen: Uniformly blackish brown, mostly dull to faintly subshiny, moderately invested with microtomentum. Male abdomen: Tergites 1+2-6 well developed, lengths of 3-6 subequal; tergite 7 well developed but narrow, band-like; sternites 3-5 well developed, rectangular, wider than long, lateral margins shallowly arched; sclerotized posterior margin of sternite 5 very shallowly emarginate, very broadly V-shaped; sternite 6 apparently lacking; sternite 7 moderately well developed, wider than long, with an oblique, posterior, thumb-like, short process, sternite not fused with tergite 7 to form an annulus. Male terminalia (Figs 82-85): Epandrium in lateral view (Fig. 82) trapezoidal, higher than wide, narrowed dorsally, anterior margin shallowly emarginate, posterior margin shallowly sinuous; surstylus almost as long as epandrium, extended from ventral margin of epandrium in nearly oblique alignment with it, in lateral view (Fig. 82) wide, robustly developed basally, anterior margin shallowly arched, posterior distinctly and step-wise angulate, forming a medial angle bearing an elongate seta, apical half robustly developed, thumb-like; hypandrium in ventral view (Fig. 83) parallel sided, elongate, narrowly bar-like; postgonite in ventral view (Fig. 83) convoluted with short lobe, little extended, bearing 3 apical setulae, lobe in lateral view narrow, longer than wide; phallus in ventral and lateral views (Figs 83, 85) mostly membranous and difficult to discern; phallapodeme in lateral and ventral views (Figs 83) elongate, parallel sided, bluntly rounded apically; ejaculatory apodeme reduced, about as long as half that of phallapodeme, longer than wide, apex slightly dilated but not fan-like. Remarks. This species is known thus far only from southern Mexico. We suspect that it will be found to be more widespread once there is better sampling from other Central American countries. It is the only species of the nigrifacies group that has a conspicuously sclerotized ejaculatory apodeme.  Head: Head ratio 0.64-0.66; frons generally brownish black to black, mostly very finely and sparsely microtomentose, subshiny to shiny, except for densely microtomentose, velvet-like anterolateral angles and anterior margin; anterolateral angles setulose; frons wider than long, frontal ratio 0.45-0.47; interfrontal seta shallowly curved, elongate, length subequal to length of lateral vertical seta. Antenna black; basal flagellomere variable but usually short, length usually not exceeding height at base, tapered to moderately acute point at apex, both dorsal and ventral margins nearly straight to very shallowly depressed dorsally and arched ventrally; pedicel with ventral projection short, length of projection conspicuously less than length of pedicel without considering projection, bearing long, ventroapical seta (extended slightly beyond apex of basal flagellomere), 1 dorsal seta, 1 dorsomedial seta, 1 medial seta; arista bearing 13-14 dorsal rays, 3-4 ventral rays. Face comparatively narrow, facial ratio 0.45-0.48; dorsad of transverse carina sparsely microtomentose, subshiny to shiny, mostly brownish black to deeply bluish black; ventrad of transverse carina densely microtomentose, silvery white, sericeous; large facial setae arranged in 2 transverse rows of 6 setae; medial pair of dorsal row widely separate, shallowly dorsoclinate; next 2 setae shallowly ventroclinate; ventral row of facial setae all ventroclinate. Clypeus black with whitish gray microtomentum; palpus brownish black.
Description of female. As in male except as follows: Head generally narrower, head ratio 0.86-89; frontal ratio 0.54-0.57; facial ratio 0.33-0.36. on the lobe of the postgonite (2-6), and the ejaculatory apodeme is generally reduced or inconspicuous. In all other species of Planinasus, the lobe of the postgonite, which is generally better developed, bears more than 20 setulae, and the ejaculatory apodeme is large, with a fan-like apical expansion. We recognize this group by the characters noted above but also by the unique structures associated with the male pre-and postabdomen. Among these characters are the apparent fusion of sternites 4+5 and a well-developed sternite 6, which is broadly produced medioposteriorly to form a shallowly bifurcate projection. In addition, the ejaculatory apodeme is short and its apex is not expanded. Head: Head ratio 0.71; frons generally brownish black to black, mostly very finely and sparsely microtomentose, subshiny, except for densely microtomentose, anterolateral angles and anterior margin; anterolateral angles setulose; frons moderately wider than long, frontal ratio 0.49; interfrontal seta shallowly curved, elongate, length subequal to length of lateral vertical seta. Scape and pedicel black; basal flagellomere pale, mostly yellowish on basal but black apically and faintly so dorsally, elongate, length much greater than height at base, tapered to moderately acute apex, dorsal margin shallow depressed, ventral margin shallowly arched; pedicel with ventral projection short, length of projection conspicuously less than length of pedicel without considering projection, bearing long, ventroapical seta (extended slightly beyond apex of basal flagellomere), 1 dorsal seta, 1 dorsomedial seta; arista bearing 13-14 dorsal rays, 3-4 ventral rays. Face comparatively narrow, facial ratio 0.35; dorsad of transverse, arched carina sparsely microtomentose, subshiny, sericeous, broad medial portion brown to brownish yellow anteriorly; antennal grooves nearly flat, brownish black; ventrad of transverse carina more densely microtomentose, yellow medially, lateral areas blackish brown; large facial setae arranged in 2 transverse rows; dorsal transverse row consisting of 1 pair of separate, well-developed, dorso-to inclinate setae; ventral row arched, comprising 6 ventroclinate setae about equidistant from peristomal margin. Clypeus black with sparse whitish gray microtomentum; palpus brownish black.
Description of female. As in male except as follows: Head generally narrower, head ratio 0.70; frontal ratio 0.56; facial ratio 0.35.
Remarks. The male abdomen of this species is atypical of other congeners in having apparent fusion of some sternites (sternites 4+5) and a well-developed sternite 6 that is broadly produced medioposteriorly to form a shallowly bifurcate projection. We have observed this condition only in this species, and our observation is limited to the single holotype male. Head: Width 0.78 mm; facial width at narrowest point 0.25 mm; frons dark brown, glabrous; interfrontal seta short, about half length of lateral vertical seta, reclinate, separated by slightly more than distance between outside margins of posterior ocelli; postocellar seta lacking; proclintate and reclinate fronto-orbital setae approximately equal in length, reclinate seta inserted slightly medial to proclinate seta, separated from latter by about 3 times its diameter at base; medial and lateral vertical setae about equal in length. Antenna bicolored, scape and pedicel brown, basal flagellomere pale, mostly whitish yellow with pale brown area immediately around base of arista; scape very thin; antennal bases separated by about diameter of pedicel; pedicel with deep anterior cleft; ventral projection of pedicel short, not extended anteriorly much beyond dorsal margin; medial half of pedicel with 2 black, stout setae of equal length, both oriented anteriad, parallel; lateral half of pedicel with thin seta dorsally, near cleft, and 4-5 fine, smaller setulae in row on anterolateral margin; flagellomere short, width about 2/3 length; arista with lateral trunk bearing 4 branches all on one side; apical branch pair smallest; main ramus of arista with 4 large dorsal branches, plus terminal fork; 4 smaller medial branches; 2 ventral branches; both rami of arista with a common base, but no common ramus. Face bicolored, mostly pale, whitish yellow, but with oral margin and narrow medial extension brown; facial setae in 2 irregular rows; setae along ventral row of larger medial setae in row along sloping line at transition between pale and brown color. 2 other facial setae inserted dorsad of longer row, between large dorsoclinate setae and anteroventral margin of eye (seta inserted closer to eye almost twice length of seta inserted between it and dorsoclinate setae). Proboscis pale; palpus thin, pale.
Type material. The holotype female is preserved in Dominican amber (Dominican Republic. specific provenance unknown) and is deposited in the AMNH (type number DR-8-208).