Nematothallus  Nematothallus is a form genus comprising cuticle-like fossils. Some of its constituents likely represent red algae, whereas others resemble lichens. "Nematothallus" was first described by Lang in 1937, who envisioned it being an early thallose land plant with tubular features and sporophytes, covered by a cuticle which preserved impressions of the underlying cells. He had found abundant disaggregated remains of all three features, none of which were connected to another, leaving his reconstruction of the phytodebris as parts of a single organism highly conjectural. Even so, it was picked up by Jonker (1973), who proposed that "Nematothallus" represented leaves of "Prototaxites", which he interpreted as a red alga. Further work failed to draw together all aspects of the organism: Edwards (1982) and Edwards and Rose (1984) both provided thorough descriptions of the cuticular aspects of the plants, while Pratt "et al." (1978) and Niklas and Smocovitis (1983) focused on the anatomy of the tubes. Indeed, some workers suggested that the name "Nematothallus" should only apply to the tubes, until Strother (1993) found more complete specimens, with tubes attached to the cuticle. He attempted to unite and formalise the genus, and extended it to include banded tubes, which are instead referred to as nematoclasts (Graham & Gray 2001). It is possible that "Nematothallus" consisted of two layers of cuticle, although fossils giving this impression may in fact represent two layers which happened to overlap one another and become stuck. It is not readily established what the cuticle represents. Lang (1945) had it as an epidermal layer, similar to the waxy cuticle of plants today, covering a parenchymatous layer. Alternatively, Edwards (1982) proposed that the inner tissue of "Nematothallus" comprised stringy tubes, with the cellular patterning produced by their ends. The genus was later formalised by Strother, who discovered better preserved and more complete specimens in Pennsylvania, America – which appear to show tubes connected to the rims of cuticle. "Nematothallus" is widespread from the late Silurian, but similar cuticle is reported from the Caradoc epoch (late Ordovician, ). It is, however, difficult to distinguish "Nematothallus" cuticle from that of arthropods.