Whittington (1975) interpreted the gills as paired extensions attached dorsally to the bases of all but the first flaps on each side, and thought that these gills were flat underneath, had overlapping layers on top.[1] Bergström (1986) revealed the "overlapping layes" were rows of individual blades, interpreted the flaps as part of dorsal coverings (tergite) over the upper surface of the body, with blades attached underneath each of them.[17][8] Budd (1996) thought the gill blades attached along the front edges on the dorsal side of all except the first flaps.