No. 440.] 



STUDIES OF GASTROPODA. 



specimens of /•'. tuberculatum, from St. Mary's river, Md., t 

 nodes are replaced in the last whorl by a continuous strong a: 

 smooth keel, while in others the nodes still persist faintly 

 the keel of the last 

 whorl. The more 

 strongly spinous types 

 of F. tuberculatum rep- 

 resent lateral radia- 

 tions. In general the 

 angular character of the 

 whorl is retained for a 

 brief period before the 

 whorl becomes rounded 

 to the 



but 



keel 



been observed between 

 the tuberculous and the 

 smooth stages. In Fu- 

 sus, on the contrary, a 

 definite keel is generally 

 formed by the consolida- 

 tion of the tubercles, as 



■ r/i\ u la 



and /•>//.-// 



ants of the present types. Kxamples <>t 

 yet be found with the final whorl rounded. 



It appears then, that there are two bran( 

 the Fulgur series, one leading to a keeled ( 

 never forming spines, the other to a smo 



rred in the Miocene t 



