MARINE M0LLUSCA OF THE UNITED STATES. 191 



Genus AVICULA, Brug. 

 Encyc. Meth., t. 177. 1793. 



LA. Atlanttca, Lamarck. Fig. 525. 



Anim. s. Vert., vii. 1822. 

 Avicula hiru ndo, Say. Journ. Acad. Nat. Sci. Philad., ii. 262. 1822. 



Shell 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. 



North Carolina, soutJiwards. 



Genus PINNA, Linnasus. 

 Syst. Nat., edit. x. 707. 1758. 



Animal with the mantle doubly fringed; foot elongated, grooved, 

 spinning a powerful byssus attached by large triple muscles to the 

 centre of each valve ; adductors both large ; palpi elongated ; gills 

 long. 



1. P. seminuda, Lamarck. Fig. 526. 



Anim. sans Vert., vii. Gl. 1822. 

 P. squamosissima, Philippi. 



Shell triangular, truncated; posterior side longitudinal]}' ribbed, 

 man}' scaled, scales delicate, erect; anterior side with the scales 

 plentiful, minute, rather obsolete towards the umbones, with a few 

 large, concentric wrinkles, dull olive. 



South Carolina, southicards. 



2. P. muricata, Linnams. Fig. 527. 



Syst. Nat., edit. xii. 11G0. 1767. 

 P. Carolinensis, Hanley. Proc. Zool. Soc. 225. 1858. 



Shell triangular, whitish, somewhat ventricose, obscurely ribbed, 

 ribs armed with triangular, erect scales. 



South Carolina, southicards. 



Family OSTPwEID^E. 



Synopsis of Genera. 



Shell irregular, attached by the left valve ; upper valve flat or concave, 

 often plain; lower valve convex/often plaited or foliaceous, and with a 

 prominent beak ; ligamental cavit} r triangular or elongated ; hinge tooth- 

 less ; structure subnacreous, laminated. Ostrea, Linnseus. 



