862 



TETRABRANCHIATE CEPHALOPODS. 



round and the lobes denticulated, as in Ceratites ; or both sad- 

 dles and lobes are incised. No " Aptychus " is present (Zittel). 

 The genera included in this family are mostly Triassic, the type- 



5j 



Fig. 782. — Turrilites catena- 

 tus. The lower figure repre- 

 sents the entire shell ; the up- 

 per figure represents the base 

 of the shell seen from below. 

 Gault. 



y* 



Fig. 783. — Baculitcs 

 ancefis, showing part of 

 the body-chamber and 

 a portion of the septal 

 chambers. Chalk. 



genus being Ptychites itself, in which the sutures have both the lobes 

 and the saddles incised. 



Family 11. Amaltheid^e. — This family includes "Ammonites," 

 in which the shell is discoidal and laterally compressed (fig. 784, 

 785), and the last whorl conceals a considerable portion of the 

 preceding volutions. The body-chamber occupies about two-thirds 



