OYK'I'OCEKAS. UNCIKJKKAS, KTO. 2 I 1 



(iciius PILOCERAS, Salter. 



Slu'll l»i(>;i(l. conic:!!. snl)cylimlrical or coiiipivsscd. sliolitly 

 curved. The siplmncle and septa represented bv a series of 

 conical septa, conca\e to a central point. 



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

 I'lLOCERAS. Ideal section. PI. DT. tio-. 4<S6. 



(Melius CYETOCERAS, (iokltiis-^. 



Shell curved ; siphuncle small, subcentral. 



Fossil, eighty-four si)ecies. L.Silurian to ("ai'l). N. a)irl S. 

 America ; Eiu^ope. 



Seems to differ hut little from Orthoceras. 

 C. ACUTicosTATUM, SandL. PI. 07, fig. 4ST. 



Subgenera : 

 Oncoceras, Hall. 



Anterior half of the shell inflated, aperture more or less 

 strangulated. This may possibly ^ Phragmoceras. Brod. 



Silurian. New York. Thi-ee species. 

 O. coNSTRiCTiJM. Hall. PI. IIT. fig. 488. 



Cyrtocerina, Billings. 



Siiell sliort and thick, with a large siphuncle, placed dorsally. 

 Two s])ecies. Silurian. Canada. 



Streptoceras, Billings. 



Shell like Oncoceras, but the aperture trilobed. 

 Two species. Middle Silnrian. Canada. 



Genus GOMPHOCERAS, J. Sowb. 



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

 aperture contracted in the middle ; siphuncle sul)central ; septa 

 simple, concave. 



100 species. L. Silurian to Oarb. Europe: N. America. 

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

 G. BoHEMicu.M, Barr. PI. 97, fig. 490. Aperture. 



