CEPHALOPODA— ORTHOCHOANITES. 



59 



47. P. trusitum (Clarke and Ruedemann). Siluric. 



Gradually tapering; septa close, from 3-6 mm. apart; sutures 

 with broad, ventral saddle. Siphuncle small, ventrocentren, nearly 

 cylindrical; striae fine, seldom preserved. 



i. f-r 



Fig. 1262. Protokionoceras tne- 

 dullareyXVz' (After Hall, 20th 

 Mus. Rep.) 



Fig. 1263. Protokionoceras crebes- 

 cens. Hall, X^- (After Hall, 20th 

 Mus. Rep.) 



