138 AMERICAN MARINE OONCHOLOGY. 



2. P. BITRUNCATA, Conrad. Fig. 321. 



(Glycimeris.) Proc. Philad. Acad., 216, t. 7, f. 1. 1872. 

 P. Americana, Conrad. Coues in Proc. Phil. Acad., 139. 1871. 



Shell short, rhomboidal, ventricose, contracted, and obliquely 

 truncated anteriorly ; posterior margin oblique, slightly emargi- 

 nate, cardinal tooth in right valve small, compressed, flattened on 

 the posterior side ; pallial sinus widely and obtusely rounded. 



Fort Macon, N. O. 



A single valve only was received by Mr. Conrad ; and I suspect 

 that it is from a submarine fossil deposit, although Mr, Conrad 

 thinks it recent. 



Genus CYETODARIA, Daudin. 

 Journ. de Phys. 1799. 



The animal is larger than the shell, subcylindrical ; mantle 

 closed, siphons united, protected by a thick envelope ; orifices 

 small; pedal opening small, anterior; foot conical; palpi large, 

 striated inside, the posterior border plain ; gills large, extending 

 into the branchial siphon. 



There are two species, extensively distributed through the Arctic 

 Seas. 



1. C. SILIQUA, Chemnitz. Figs. 316, 31 Y. 



(My a.) Conch. Cab., xi. 192, t. 198, f. 1934. 

 Glycimerus incrassata, Lamarck.- Syst. An. s. Vert., 126. 



Transversely oblong, compressed, heavy and solid ; epidermis 

 thick, shining, obliquely wrinkled ; beaks not prominent, eroded ; 

 ligament large, prominent on the shorter end. Interior with a 

 very thick callus in the course of the pallial impression ; callus of 

 the hinge broad and prominent. Shining black ; under the epi- 

 dermis ashen gray. 



Length 3.5, height 1.5 inches. 



Massachusetts, northwards. (Eur.) 



Genus SOLEMYA, Lamarck. 

 Anim. s. Vert., v. 488. 1818. 



The mantle lobes are united behind, with a single, hour-glass 

 shaped, cirrated, siphonal orifice ; foot proboscidiform, truncated 

 and fringed at the end ; gills forming a single plume on each side, 

 with the laminae free to the base ; palpi long and narrow, nearly 

 free. 



The animal is very active, leaping and swimming rapidly. The 



