MUSEUM OF COMPARATIVE ZOOLOGY. 307 



sense, as has been done by some concbologists; since, if it has the right to be 

 used at all, it is entitled to take precedence of Thracia as the primary name of 

 the group. 



There are several species of Thracia, not including the plaited Cyathodonta 

 of Conrad, formerly referred to Thracia, which inhabit the southern and south- 

 eastern coasts of the United States and adjacent waters. Most of them have 

 not been definitely recognized hitherto. They are: — 



Thracia Stimpsoni, u. s. 



Thracia corbuloidea Blainville. 



Thracia distorta Montagu. 



Thracia phaseolina Lamarck. 



Thracia Stimpsoni, n. s. 



Thracia Stimpsoni is a magnificent species, nearly as large as T. Cunradi, 

 and of which but one right valve has yet been obtained, between Tampa and 

 Tortugas in 28 fms. in the Gulf of Mexico. It difl'ers from T. convexa Wood, 

 which is its nearest relative, in its whiter and much more coarsely granulose 

 surface, in its more horizontal posterior hinge-margin not rounded off at its 

 posterior end, and by two strong ribs, one of which extends parallel with the 

 posterior hinge-line, bounding a narrow smooth depressed marginal area, and 

 having a wider depressed broad ray on the outer and lower side; the other rib 

 extends from the beak to the lower posterior angle of the rostrum ; in front 

 of it the shell is much depressed, behind it elevated for a space extending to 

 the depressed ray above mentioned; the middle basal margin is more produced 

 than in T. convexa, and the pallial sinus is shallower and less angular. The 

 other proportions are about the same as in T. convexa. 



The specimen in the National Museum is 65.0 mm. long, and is named in 

 honor of the late Dr. William Stimpson. 



Thracia corbuloidea Blainvillb. 



Thracia corbuloidea Blainville, comparing excellently well with the series 

 in the Jeffreys collection, has been obtained by the U. S. Fish Commission 

 in from 15 to 50 fms. off the coast of North and South Carolina, generally, 

 about twenty miles from shore. I have it also from Key West, collected by 

 Hemphill. 



Thracia distorta Montagu. 



Thracia distorta Montagu, has been sent me from Honduras by Mr. Charles 

 T. Simpson, who was formerly resident there. It does not exactly agree with 

 any particular specimen from British seas, but differs from most of them less 

 than they differ among themselves. It is possible that this may be the same 



