MARINE MOLLUSCA OF THE UNITED STATES. 161 



directed forwards. Anterior lunule heart-shaped, distinctly 

 marked by a simple line. Epidermis dingy white. 

 Length 43, height 35 mill. 



New England and Middle States. 



The true C. convexa of Say is a different species, only occurring 

 fossil. 



Genus DOSINIA, Scopoli. 



The siphons are united ; mantle-margin plicate ; foot subquad- 

 rangular, without a byssal groove. 



1. D. DISCUS, Reeve. - Fig. 399. 



Monog. Conch. Icon., vi. sp. 9. 

 Artemis concentrica, Conrad (not Gmelin), Mar. Conch., t. 12. 



Shell compressed, with fine, regular, impressed concentric strise ; 

 beaks considerably curved, pointed ; lunule cordate, slightly im- 

 pressed ; epidermis yellowish-white; hinge with a large oblong 

 fosset under the beaks ; muscular impressions very large. 

 Length and height 3.5 inches. 



Virginia to West Indies. 



Genus TAPES, Muhlfeldt. 

 Entwurf. 51. 1811. 



Siphons united as far as the middle, diverging at their ends ; 

 branchial siphon crowned with arborescent tentacles; mantle- 

 margin simple ; foot lanceolate, byssiferous. 



1. T. FLUCTUOSA, Gould. Figs. 400, 401. 



(Venus.") Invert. Mass., 1st edit. 87. 1842. 

 Venus Astartoides, Beck. Middend. Beitr. Mai. Ross., iii. 56. 1849. 



Shell transversely ovate, thin, lenticular, white, with a yellow- 

 ish epidermis; surface with recurved concentric waves vanishing 

 at the sides ; areola none, or indistinct in old specimens. 



Length 20, height 15 mill. 



Newfoundland, northward. 



Genus PETEICOLA, Lamarck. 

 Syst. Anim. s. Vert. 121. 1801. 



Siphons elongated, distinct, their orifices ciliated; the mantle- 

 lobes are united except a small anterior opening ; foot compressed, 

 lanceolate, with a byssiferous fissure a little behind the middle of 

 the lower edge. 



The Petricolas excavate limestone or coral rocks, and also bury 

 in mud. 

 11 



