| Abstract: | Several specimens of an elasmobranch from the upper Mississippian Bear Gulch limestone of Montana are described. The first dorsal spine and fin closely resemble Stethacanthus erectus and to a lesser extent Stethacanthus altonensis. The new genus and species Orestiacanthus fergusi is proposed for the specimens, and it is suggested that recent attempts to synonymize the species of Stethacanthus on the basis of spines are unjustified. The specimens also share the enlarged cranial denticles, general form of the palatoquadrate, cladodont teeth and pectoral fin with S. altonensis. They differ from S. altonensis in proportions of jaws, numbers of tooth families, numbers of prearticular basals and axial radials, morphology of the second dorsal fin, and in the presence of generalized squamation in some specimens (but not the female). The pelvic fins differ greatly in having a prominent metapterygium. |
