MARINE MOLLUSCA OF THE UNITED STATES. 161] 
directed forwards. Anterior lunule heart-shaped, distinctly 
marked by a simple line. Epidermis dingy white. 
Length 48, 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. piscus, 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 strix ; 
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, 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. 
1. T. rLuctuosa, Gould. Figs. 400, 401. 
( Venus.) Invert. Mass., 1st edit. 87. 1842. 
Venus Astartoides, Beck. Middend. Beitr. Mal. 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 PETRICOLA, 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. 
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