CEPHALOPODA— AMMONOIDEA. 201 



rated by wider concave interspaces and scarcely enlarging towards 

 the venter. 



Nanaimo of Sucia and Hornby Islands, British Columbia; also 

 Japan. 



CLVI. Ptychoceras d'Orbigny. 



Similar to Hamites, but the straight limbs in contact, or im- 

 pressed upon one another, the ribs smooth or tuberculated ; suture 



F[G. 1464, a, Ptychoceras meekanujn, lateral view, and b, c, P. ( Oxybeloceras) 

 crassum, lateral and dorsal views. (After Whitfield.) 



much simpler than that of Hamites and suggesting a closer rela- 

 tionship to Baculites. Comanchic-Cretacic. 



350. P. (Oxybeloceras) crassum Whitfield. (Figs. 1464, b, c; 

 1466.) Cretacic. 

 Ribs distant, .sharp, oblique, ending in spinous nodes on either 



side of a broad, concave, ventral groove ; whorls slightly impressed. 

 Pierre of Black Hills. 



351. P. meekanum Whitfield. (Figs. 1464, a; 1465.) Cretacic. 

 Of somewhat oblate, transverse section, smaller than preceding, 



Fig. 1465. a, Piychoceras meeka- 

 num, X 2. 



Fig. 1466. Piychoceras ( Oxybeloceras') 

 crassum, X 2. 



