OYRTOCERAS, ONCOCERAS, ETC. "2 1 1 



Genus PILOCERAS, Salter. 



Shell broad, conical, subcylindrical or compressed, slightly 

 curved. The siphuncle and septa represented by a series of 

 conical septa, concave to a central point. 



Fossil, three species. L. Silurian. Canada; Scotland. 

 PILOCERAS. Ideal section. PI. 97, fig. 486. 



Genus CYRTOCERAS, Goldfuss. 



Shell curved; siphuncle small, subcentral. 



Fossil, eighty-four species. L. Silurian to Carl). N. and $. 

 America ; Europe. 



Seems to differ but little from Orthoceras. 

 C. AcuTicosTATi.'M, Saiidb. PI. 97, fig. 487. 



Subgenera : 

 Oncoceras, Hall. 



Anterior half of the shell inflated, aperture more or less 

 strangulated. This may possibly = Phragmoceras. Brod. 



Silurian. New York. Three species. 

 O. CONSTRICTUM. Hall. PI. 97, fig. 488. 



Cyrtocerina, Billings. 



Shell short and thick, with a large siphuncle, placed dorsally. 

 Two species. Silurian. Canada. 



Streptoceras, Billings. 



Shell like Oncoceras, but the aperture trilobed. 

 Two species. Middle Silurian. Canada. 



Genus GOMPHOCERAS, J. Sowb. 



Shell fusiform or bottle-shaped, straight, swollen anteriorly ; 

 aperture contracted in the middle ; siphuncle subcentral ; septa 

 simple, concave. 



100 species. L. Silurian to Carb. Europe; N.America. 

 G. PYRIFORME. PL 97, fig. 489. Silurian. England. 

 (1. BOHEMICUM, Barr. PI. 97, fig. 4!)0. Aperture, 



