90 



margin of one valve, closes over tliat of the other. This species 

 is very different from the P. msequivalvis, particularly in having 

 the hinge placed much fixrther back, and consisting of a mere 

 angle, not prominent ; the rostrum also has a direction more up- 

 ward. 



AviCULA HIRUDO. — Var. Shell perlaceous; epidermis reddish- 

 brown, with very numerous undulated wrinkles, which are disposed 

 in radii, and rendered more conspicuous by a white longitudinal 

 line at the junction of each series of wrinkles with its contiguous 

 one. 



Width about three-fourths of an inch. Inhabits the southern 

 coast. Cabinet of the Academy and Philadelphia Museum. 



It appears to be rare. I have found but a single entire speci- 

 men, which is young. In its radiating series of wrinkles, it ap- 

 proximates to A. morio of Leach, but differs from it in magnitude, 

 and in being radiated with whitish lines. I have a specimen from 

 the West Indies, which corresponds very well with this, but as it 

 is a much older shell, it is of a much darker color, and the radii 

 are interrupted into abbreviated lines. 



A valve of an adult shell also occurred on the southern coast, 

 but so much worn by attrition that its superficial characters are 

 destroyed. 



Mytillus cubitus. — Shell oblong, striated with elevated, sub- 

 glabrous lines, which are smaller on the anterior side; anterior 

 edge linear, or slightly concave ; posterior edge ascending from the 

 base in a right line to a prominent angle, which is rather behind 

 the middle of the shell, from which it descends by a concave line 

 to the obliquely and very obtusely rounded tip ; color yellowish, 

 polished and somewhat facciated with green or brownish, which 

 disappear on the anterior margin. 



Length one and one-fifth of an inch. Breadth half an inch. 

 Inhabits the coast of the United States. Cabinet of the Academy 

 and Philadelphia Museum. 



This species, seems to bo most closely allied to M. demissiis and 

 exustus; from the former it is distinguished, by not having the 

 angle on the posterior side obtusely rounded, and not placed con- 

 siderably before the middle ; and the line of the edge before this 

 angle, is not convex as in that shell. It does not at all correspond 

 with the figures in the Encyc. Method, which are quoted for extis- 



