FOSSILS OF THE POTSDAM GROUP. 227 



feature may have been wrongly interpreted, as the specimen is mutilated 

 and somewhat obscure. Axial lobe- narrow and moderately elevated ; less 

 than two-thirds of the entire length of the shield; marked by ten very short 

 annulations, exclusive of the terminal ones. Lateral lobes moderately con- 

 vex in the middle and becoming flattened toward the margin ; marked by 

 five simple, faint ribs on each side, exclusive of the anterior one, which is 

 also the most prominent and angular. The posterior border has the appear- 

 ance of having been produced at the extremity into a broad, flattened, tri- 

 angular process, or spine ; and judging from another individual, apparently 

 of the same species, has had two other points or digitations on each side, 

 one at the lateral angle and the other just below, leaving a deep, broad 

 sinus between it and the central point. 



The specimen has some resemblance to small convex examples of B. 

 Minnesotensis Owen, but differs in the more arcuate anterior border, extended 

 posterior extremity, and greater number of rings on the axis. From D. 

 Pepinensis Owen, it differs in the stronger axis, more numerous rings, sim- 

 ple ribs of the lateral lobes, and in the form of the posterior lateral margins. 



Formation and locality. — In limestone of the Potsdam group, in the 

 Eureka District, Nevada. Collected by Arnold Hague, esq, 



DlKELLOCEPHALUS FLABBLLIPER n. Sp. <?^ 



Plate II, figs. 29-30. 



A small pygidium occurring in a fragment of dark-colored limestone, 

 associated with those containing Conocephalites laticeps, Bathyurus fangulatus, 

 and Chariocephalus tumifrons, but probably from a different layer, judging 

 from the lithological characters of the specimens, has a character so marked 

 and peculiar that it has been deemed worthy of notice. The specimen pos- 

 sesses the following characters : 



Pygidium transversely semicircular, the length and width being as 

 three to seven ; front margin slightly arcuate to near the outer extremities, 

 where it curves somewhat abruptly backward to the point of the first digi- 

 tation. Posterior margin digitate, having three points on each side, and a 

 central one ; digitations broad and obtuse, the middle one on each side the 

 largest. Axial lobe of moderate strength, highly convex, faintly subangular 



