28 INVERTEBRATA OF MASSACHUSETTS. 



27, t. 3, f. 4. WOOD; Gen. Conch., 81, pi. 15, f. 3-5. Index, pi. 2, f. 5. 



DILLWYN; CataL, 40. DKSHAYES; Encyc. Milk, Vtrs, iii. 754, pi. 169, 



f. 5, 7. LAM.; An. sans Pert., vi. 46. SCHROET. ; Einl. in Conch., iii. 



541, No. 6. 



Pholas bifrons, DA COSTA ; Brit. Conch. ,243, t. 16, f. 4. 

 Pholas latus, LISTER ; Conch., t. 436, f. 279, and Append., t. 10, f. 3. 



Shell oblong-oval, thick and strong, rounded posteriorly, nar- 

 rowed anteriorly into a sort of beak ; widely gaping at both ends, 

 the valves touching each other only at two points, viz. the hinge, 

 and the middle of the base. Exterior surface marked with 

 numerous coarse, concentric ridges, which become lamellar on 

 the anterior half ; the laminae are strongly toothed on their free 

 edge, and the teeth are disposed in radiating series. The. valves 

 are divided into two nearly equal portions by a broad channel 

 running from the beaks to the middle of the base. Interior 

 smooth, showing the external furrow, the upper and anterior edge 

 turned outwards so as to present large, smooth callosities over 

 the beaks. The process from within the cavity of the beaks is 

 large, narrow, and a little flattened at the tip. Length 2 inches, 

 height 1J inch. 



A very perfect specimen of this shell is in the cabinet of Dr. S. Bass, 

 which was found at Phillips's Beach. Young specimens were found in 

 hard clay at Phillips's Beach by Mr. Joseph True. They differ princi- 

 pally in gaping only anteriorly. Full grown valves are occasionally 

 thrown up on all our beaches ; but it is more common at the South, as 

 along the shores of New Jersey. When alive, a membranous expan- 

 sion covers the superior border of the shell. 



FAMILY SOLENACEJl, LAM. 



Shell transversely elongated, without accessory pieces, and gaping only at 

 the ends* 



GENUS SOLEN, Lm. 



Shell equivalve, elongated, sides nearly parallel, gaping at both 

 ends ; beaks very small, terminal ; cardinal teeth small, rounded, 

 variable. 



SOLEN ENSIS. 



Shell six times as long as high, curved, front and back parallel, 

 smooth, yellowish-green ; hinge with one tooth and a sharp lateral 



