NYMPH ACE A. 339 



Psammohia, Galeommay Tellina, Corhis, Lucina, Do'na.v, and 

 Capsa. 



The shell of Sangidiiolaria is equivalve^ inequilateral, 

 transverse, somewhat elliptic, compressed, thin, and a little 

 gaping at both sides; the margins are curved, and not 

 parallel. Two cardinal teeth are situated close to each 

 other in each valve, sometimes bifid, also a prominent tes- 

 taceous appendage or fulcrum on the umbonal margin. 

 The muscular impression of the mantle exhibits a large 

 sinus. 



The genus Psaimnohia, which connects Sanguhiolana and 

 Tellina, is chiefly characterized by the shell being always 

 more or less angular at one end, with the cardinal teeth 

 short, and mostly bifid. 



The shell of the genus Gcdeomma is thin, small, oblonsro- 

 ovate, equivalve, equilateral, and gaping at the ventral 

 margin. One cardinal tooth belongs to each valve ; liga- 

 ment small, duplex, partly internal, and partly external. 



The shell of Tellina is transverse or orbicular, nearly 

 equivalve, flat, and having the anterior side somewhat beaked 

 or angular, and in general irregularly flexuose at the ventral 

 margin. Two lateral and two cardinal teeth belong to each 

 valve; the former, however, are often remote, sometimes 



