MARINE MOLLUSCA OF THE UNITED STATES. 12 Y 



minutely striated transversely and longitudinally, and having 

 about twelve cells. 



Transverse axis 4J, vertical 1 J inches. 



/So. Carolina to West Indies. 



Yery common on the southern coast, penetrating compact mud 

 or clay. It cannot be distinguished from D. Chiloensis, King, a 

 species inhabiting the west coast of South America. 



Genus ZIBPHJEA, Leach. 

 Gray, Ann. and Mag. Nat. Hist., 2d ser. viii. 385. 1851. 



1. Z. CRISPATA, Linnaeus. Figs. 265, 265, and 266. 



(Pholas.) Syst. Nat., edit. xii. 1111. 1767. 

 PJiolas semicostata, H. C. Lea, Bost. Journ. Nat. Hist., 285, t. 24, f. 1. 



Shell large, thick and strong, oval-oblong, rounded behind, sub- 

 angular or beaked in front ; both extremities widely gaping, the 

 valves touching only at the hinge and middle of the basal mar- 

 gin ; surface divided into two portions by a broad furrow, running 

 almost vertically from the beaks to the base ; the anterior portion 

 coarsely marked with lamellar concentric plates; within smooth, 

 but showing the outer broad vertical furrow ; soiled grayish-white, 

 occasionally rust-colored. 



Transverse axis 2.5, vertical 1.5 inches. 



Northern United States. (Eur. ) 



Subfamily JONANNETINJ3, Tryon. 

 Proc. A. N. S. Philad. 1862. 



Genus MAETESIA, Leach. 

 Blainville, Diet. Sc. Nat. 1824. 



1. M. CUNEIFORMS, Say. Figs. 26Y, 268. 



(Pholas.) Journ. Philad. Acad., ii. 322. 1822. 



Wedge-shaped; anterior margin nearly closed, transversely 

 truncated from the hinge ; posterior margin with a rounded lip ; 

 a deep furrow from the beak to the middle of the basal margin, 

 impressed within; surface with transverse undulating striae, with 

 elevated minutely crenate lines ; hinge callus, forming a cavity 

 before, and without cells; dentiform process filiform, incurved; 

 hinge plate ovate-triangular, with a short projecting angle on the 

 anterior middle, and subacute behind ; white. 



Transverse axis 20, vertical 11.25 mill. 

 (Penetrating wood.) Southern Coast; New Haven, Conn. (Perkins.) 



