MARINE MOLLUSCA OF THE UNITED STATES. IGl 



directed fonvnrds. Anterior lunule heart-shaped, distinctly 

 marlved by a simple line. Epidermis dingy white. 



Length 43, height 35 mill. 



Neio England and Middle States. 



The true G. convexa of Say is a different species, only occurrinj, 

 fossil. 



Genus DOSINIA, Scopoli. 



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

 rangular, without a b^'ssal groove. 



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



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

 Artemis concentrica^ Conrad (not Gmclin), Mar. Couch., t. 12. 



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

 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. 



Virrjiiiia to West Indies. 



Genus TAPES, Miihlfeldt. 

 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. 



L T. FLUCTUOSA, Gould. Figs. 400, 40L 



{Venus.) Invert. Mass., 1st edit. 87. 1843. 

 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. 



Neidfo^mdland, northward. 



Genus PETRICOLA, Lamarck. 

 Syst. Anhn. 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 b^'ssiferous fissure a little behind the middle of 

 the lower edge. 



The Petricolas excavate limestone or coral rocks, and also bur}- 

 in mud. 

 11 



