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\'bc " 



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; l.l., lateral lobe; l.s., lateral saddle; 

 limb., 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, + ttes, 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 ciit parallel to the plane of coiling ; note 

 siphuncle, sutures, ribs, septa. 



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

 occupy during life ? Compare with gastropods. 



