112 



taken, and which were found by Mr. Augustus Jessup. It is 



distinguishable from C. similis by its more rhomboidal form. 



Cyclas partumeia. — Shell thin and fragile, transversely-sub- 

 orbicular, with small, irregular, inequidistant, concentric wrinkles, 

 and larger adventitious undulations; base rounded; anterior and 

 posterior edges nearly central ; hinge teeth prominent and distinct ; 

 lateral teeth prominent, white ; within impressed by the exterior 

 undulations, and bluish-white on the margin and submargin. 



Length nine-twentieths; breadth eleven-twentieths of an inch. 



This species was found by Mr. William Hyde, in a pond near 

 (lermantown, in plenty. In comparison with C. similis, it is 

 thinner, more transparent, not flattened at base, more obtusely 

 rounded each side, and instead of grooves of some degree of regu- 

 larity as in that shell, it is sculptured with irregular wrinkles and 

 waves. Mr. Hyde took fifty young ones out of a single specimen- 



N. B. The genus Cyclas was inserted into this essay inad- 

 vertently ; the species, however, are new.* 



[*The title of the paper being " Description of Univalve, &c., Shells. 

 —Ed.] 



[J. A. N. S. vol. iv. p.. 368, et seqq., 1825.] 



MoDiOLA. — Amongst a number of marine shells from the island 

 of Minorca, presented to the Academy by Dr. Alexander Mont- 

 gomery, of the U. S. Navy, is a single valve of the Pecten nodosus, 

 Linn., on which were several elevations that, on a cursory glance, 

 presented an appearance not unlike the Balanus. On a more par- 

 ticular inspection, each elevation proved to be similar to the others 

 in form and consistence, and to be composed of fine dark colored 

 sand, agglutinated together, attached by a broad base to the surface 

 of the Pecten, and rising in the shape of a very low cone around 

 an included shell, the visible portion of which is exactly cordate. 

 Having carefully detached the mass, I found the imbedded shell 

 to be a Modiohi, closely allied to the discors, Gmel., with its byssus 

 very firmly aflixed to the supporting surface. 



The following is a description of this shell : 



MoDiOLA OPIFEX. — Oval, reddish-brown; anterior hinge-mar- 

 gin flattened, cordate ; within iridescent. 



Base contracted behind the middle, the contraction not wide 



