MOLLUSCA — CEPHALOPODS 



265 



1. Sketch (a) circular view of specimen showing sutures; 

 (b) view showing aperture. 



2. What is the relation between septum and suture ? 



3. Under what conditions do sutures become visible? 



Umb\'K 



A 8 



Fig. 117. — An ammonite, Muensteroceras oweni Hall, abounding in the ocean cover- 

 ing Indiana during Kinderhook (Lower Mississippian) time. Natural size. A , side 

 view. B, ventral view. Sutures goniatitic ; /./., lateral lobe ; l.s., lateral saddle ; 

 umb., umbilicus ; v.l., ventral lobe ; v.s., ventral saddle. (Redrawn from Hall.) 



Scaphites (Fig. 119). Cretaceous. 



Coiled in a plane spiral with the whorls in contact and embrac- 

 ing, except the last, which often becomes somewhat uncoiled 

 and detached from the spiral and recurved in the form of a 

 hook. Surface ornamented with bifurcating ribs which often 

 bear tubercles ; ribs continuous across the venter. Sutures 

 generally much divided with several auxiliary lobes. Name from 

 Greek scaphe, a boat, + ites, meaning stone, in reference to the 

 shape. 



The variety S. nodosus brevis is exceedingly abundant in the 

 Cretaceous of the Rocky Mountain region, also in New Jersey. 



1 . Sketch (a) view of spiral ; (b) apertural view ; (c) interior of 

 section of entire shell cut parallel to the plane of coiling ; note 

 siphuncle, sutures, ribs, septa. 



2. How mlich of the entire shell did the body of the animal 

 occupy during Ufe ? Compare with gastropods. 



