Description of Eight new Species of Shells. 107 



resemblance to the Venus gemma of Totten. Indeed I consid- 

 ered it as such for some time, until 1 was able to obtain a view 

 of the teeth, which prove it to be a Cyrena. It may, however, 

 be also distinguished from the Venus gemma, by its equilateral 

 form, and want of crenulations on the margin. The beaks are 

 rounded at the summit. It has usually a dark purple mark along 

 the posterior margin, which gradually fades off, and the anterior 

 portion of the shell is whitish. Occasionally, however, it is 

 nearly all purple, but darker towards the posterior margin, and I 

 have one specimen which is pinkish. The striae are perfectly 

 regular, and at even distances. It is, I believe, the smallest Cy- 

 rena yet noticed. 



Genus Modiola. — Lamarck. 



M. elliptica. PI. 1, fig. 2. 



M. testa transversa, elliptica, sub-inflata, pellucida, purpureo- 

 maculata, polita, radiatim striata postice et antice ; valvulis tenui- 

 bus ; natibus sub-prominentibus ; margine crenulato postice ac 

 antice ; margarita diaphana et nitente. 



Shell transverse, elliptical, sub-inflated, pellucid, marked with 

 purple, polished, radiately striate posteriorly and anteriorly ; 

 valves thin ; beaks somewhat prominent ; margin crenulated 

 posteriorly and anteriorly ; nacre diaphanous, shining. 



Length -075. Breadth -1. Diam. -025 of an inch. 



Hab. Delaware Bay. Cabinet of I. Lea. 



Remai'ks. — The area of the valves is divided into three fan- 

 shaped compartments by the striae, of which the anterior con- 

 tains about seven, and the posterior about twenty-four. The 

 purple marks in some specimens are so numerous, as to completely 

 cover the shell, while others are nearly free from them. They 

 are frequently zigzag. The dorsal margin appears to be slightly 

 crenulate. It is strongly allied to the Modiola discors, nexa and 

 discrepans, and might be confounded with the young of either 

 of those shells. But its size appears constant, as I have taken 

 them at various seasons of the jeav ; in addition to which the 

 difference in shape and marking, and the want of transverse strias; 

 will distinguish it. 



M.pulex. PI. 1, fig. 3. 

 M. testa transversa, obovata, laevi, polita, viridescente, diaphana, 

 lineis purpureis ornata ; valvulis tenuibus ; natibus sub-promi- 

 nentibus, sub-acutis. 



