Modification of the Apex in Gastropod Mollusks. 695 



(four of them) are nodular. The apex of the first nuclear whorl 

 is a flattened hemisphere. The nodules of the post-nuclear whorls 

 begin quite abruptly. The color is yellowish white. But two 

 specimens of this species have been examined. 



Subgenus TRITONIDEA Swainson. 

 Pisania tincta Conrad. 



The nucleus is very similar in form to that of pusio, but is 

 spermaceti-white instead of yellowish or brownish. The number 

 of whorls is the same in both species. A half dozen specimens 

 examined, one of which had a dark brown apex. 



Genus EVTHRIA Gray. 

 Eutbria cornea Linn^. (Fig. 35.) 



The apex of this species is very like that of Pisania, excepting 

 that it is more oblique, the first whorl is smaller in comparison 

 with the second and the post-nuclear whorls are ribbed instead of 

 nodulous. It is brownish in color and has one and a-half whorls. 

 But a single example has been examined. 



Family NASSIDJE. 

 Genus IVASSA Lamarck. 

 STassa glans Lamarck. (Fig. 36. ) 



Apex small, rounded, smooth, consisting of one and a-half glossy 

 whorls, rapidly and regularly increasing in size. The initial 

 whorl is very small and knob-shaped with its apex bent in, and the 

 second whorl is flatly rounded. The post-nuclear whorls are 

 strongly nodulous, there being four nodules to each longitudinal 

 rib. The line between the nuclear and post-nuclear whorls is very 

 sharply drawn. About four and a-half post-nuclear whorls are 

 nodulous, and then they become smooth and polished. The nu- 

 cleus is of a rich wine color. Only a single example has been ex- 

 amined. 



Nassa triTittata Say. (Fig. 37.) 



The apex of this species is very like that of glans excepting 

 that it has two whorls and is white in color. All of the post- 

 nuclear whorls are strongly nodulate and spirally-lirate, giving 

 the shell a latticed appearance. The writer has examined three 

 perfect specimens. 



