THE NAUTILUS. 41 



mining its true position with final certainty. Obviously, how- 

 ever, it is not a Tkysanophora, nor is it a Gastrodonta. It 

 cannot well be a Sagda, nor Odontosagda, yet it seems to be 

 closely related to both. Its very prominent character of a 

 centrally placed continuous lamella on the parietal wall I 

 think justifies the creation of a genus to include it within 

 the subfamily Sagdincc. I therefore propose for it the new 

 genus, to be described for the present as follows: 



VOLVIDENS, n. g. 



Shell small, depressed, widely umbilicate, rather thin and 

 shining and of Zonites-like texture. Aperture with an inter- 

 nal sharply raised lamella centrally placed on the parietal 

 wall. Lip simple. Type : Helix tichostoma Pfr. 



This lamella in fully adult specimens extends back about 

 one-half whorl. Back of this it appears to have been absorbed 

 but there are evidences of its existence from the early whorls. 

 It differs from all the Proserpinella group by its lack of an 

 apical callus. 



I have not infrequently found in collections among lots of 

 V. tichostoma specimens of Strobilops hubbardi. To the 

 naked eye the two species appear very much alike, but they 

 can never be confused when examined under a glass. I have 

 seen no mention of the presence of this latter species in Cuba, 

 but I have found it in many localities in Havana and Pinar 

 del Rio Provinces, and it is quite likely it will be found 

 throughout the Antilles. Cuban specimens are smaller than 

 those from Florida, but otherwise identical. 



STUDIES IN NAJADES. 



BY A. E. ORTMANN. 



(Continued from page 34.) 



Genus : SYMPHYNOTA, subgenus ALASMENOTA nov. subgen. 



This new subgenus is proposed for the species : Margaritana 

 holstonia Lea as type, which has been placed by Simpson 



