MOLLUSC A. 



223 



thickened, expanded, and ornamented, as in the Wing- 

 shell (Strombus) of the West Indies ; or the interior of 

 the shell may be also modified by the removal of part 

 of the material of the old whorls inside, as happens in 

 the cowries. In such forms, some care is required to 

 identify the younger shells as of the same species with 



Fig. 76.— Shells of Siphonostomatous Gasteronods. 1, The Fountain-slieU, 

 Strombus gigas^ one-third the natural size ; 2, The Money-oowry , Cyprisa mtmeta, 

 natural size. 



the older ones. The increase of the width of the 

 whorl, in some kinds, takes place more quickly in the 

 female, so that the shell is wider in form. In these 

 cases care is also required to identify the two forms 

 as belonging to one species. 



In some shells the exterior is ornamented with 



