and wear marks indicative of its usage in feeding. H. ergassimon is also represented by several other specimens from the Phosphoria Formation, though none of these show wear marks. This species is roughly intermediate between the two contrasting forms represented by H. bessonowi and H. davisii, having tall but narrowly-spaced teeth. Its teeth are also gently curved, with obtusely-angled tooth bases. Other material Several large whorls are difficult to assign to any particular species group, H. svalis among them. IMNH 14095, a specimen from Idaho, appears to be similar to H. bessonowi, but it has unique flange-like edges on the apices of its teeth. IMNH 49382, also from Idaho, has the largest known whorl diameter at for the outermost volution (the only one preserved), but it is incompletely preserved and still partially buried. H. mexicanus, named by F.K.G. Müllerreid in 1945, was supposedly distinguished by its tooth ornamentation. Its holotype is currently missing, though its morphology was similar to that of IMNH 49382. In the absence of other material, it is currently a nomen dubium. Vladimir Obruchev described H. karpinskii from two teeth in 1953. He provided no distinguishing traits for this species, thus it must be regarded as a nomen nudum. Various other indeterminate Helicoprion specimens have been described from Canada, Japan, Laos, Idaho, Utah, Wyoming, and Nevada. In 1922, Karpinsky named a new species of Helicoprion, H. ivanovi, from Gzhelian (latest Carboniferous) strata near Moscow. However, this species has subsequently been removed from Helicoprion and placed as a second species of the related eugeneodont Campyloprion. Historical reconstructions Earliest reconstructions Hypotheses for the placement and identity of Helicoprion's tooth whorls were controversial from the moment it was discovered. Woodward (1886), who referred the first known Helicoprion fossils to Edestus, discussed the various hypotheses concerning the nature of Edestus fossils. Joseph Leidy, who originally described Edestus vorax, argued that they represented the jaws of "plagiostomous" (chondrichthyan) fish. William Davies agreed, specifically comparing it to the jaws of Janassa bituminosa, a Permian petalodont. On the other hand, J.S. Newberry suggested that the jaw-like fossils were defensive spines of a stringray-like fish. Woodward eventually settled on E.D. Cope's argument that they represented pectoral fin spines from fish similar to "Pelecopterus" (now known as Protosphyraena). Karpinsky's 1899 monograph on Helicoprion noted that the bizarre nature of the tooth whorl made it difficult to reach precise conclusions on its function. He tentatively suggested that