MARINE MOLLUSCA OF THE UNITED STATES. 127 
minutely striated transversely and longitudinally, and having 
about twelve cells. 
Transverse axis 43, vertical 1} inches. 
So. Carolina to West Indies. 
Very 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 ZIRPH#A, Leach. 
Gray, Ann. and Mag. Nat. Hist., 2d ser. viii. 885. 1851. 
1. Z. orntspaTA, Linneeus. Figs. 265, 265, and 266. 
(Pholas.) Syst. Nat., edit. xii. 1111. 1767. 
Pholas 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. 
Subfamily JONANNETIN A, Tryon. 
Proc. A. N. 8. Philad. 1862. 
Genus MARTESIA, Leach. 
Blainville, Dict. Sc. Nat. 1824. 
1. M. cuNEIFoRMIS, Say. Figs. 267, 268. 
(Pholas.) Journ. Philad. Acad., ii. 822. 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 stris, 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.) 
