MACTRACEA. MOLLUSCA. MONTActfTA. 59 



cut posterior side ; its very peculiar outline when viewed with the 

 beaks presenting, on account of its thickness anteriorly; and its 

 strong, curved, nearly smooth lateral teeth. 



GENUS MONTACUTA, TURTON. 



Shell ovate or oblong, equivalve, inequilateral, nearly closed ; 

 hinge with two teeth in each valve, and a cavity between them ; 

 lateral teeth none. 



This genus with the following, seems to have been adopted by 

 several distinguished conchologists. There appears, however, no 

 very good grounds for separating them. The genus Tellimya of 

 Brown, which comprehends them both, may yet supersede them. 

 Fleming conjectures that they are merely the fry of Mya and Lu- 

 traria ; but in this I think he is in error. None of the shells 

 found on our coasts could ever have originated from such forms. 

 Montacata would probably come under Ungulina, and Kellia un- 

 der Erycina, of Lamarck. 



MONTACU'TA BIDENTA'TA. 



Shell minute, white, ovate-triangular ; surface roughened with 

 loose lines of growth, beaks pointed ; tooth on the shorter side oblique 

 and excavated for the reception of the ligament. 



State Coll., No. 215. Soc. Cab., No. 2320. 



Mya bidentkta, MONTAGU ; Test. Brit., 44, t. 26, f. 5. MATON and RACKETT; 

 Lin. Trans., viii. 41. PENNANT; Brit. Zool., iv. 166. WOOD; Gen. Conch., 

 99. Index, pi. 3, f. 16. DILLW*N; Catal., 45. TURTON ; Conch. Diet., 102. 

 Biit. Biv.,6Q. 



Shell minute, fragile, white within and without, ovate-triangu- 

 lar, inequilateral, rather convex ; beaks nearest the broader end, 

 acute and prominent, pointing to the longer end ; upper margin 

 sloping rapidly from the beaks, ends regularly and bluntly rounded, 

 base scarcely curved ; surface shining, but rendered somewhat 

 scabrous or rough by numerous, loosely cohering edges of the 

 stages of growth ; its only variation in color consisting in the 

 opacity or transparency of its substance. Within, polished, and 



