Fam. 20.] NATURAL HISTORY SOCIETY. 101 



the shell ; ventral margin slightly rounded ; basal edge crenulated 

 within ; pallial sinus deep ; surface with radiating and concentric 

 strise. Pale, livid, with or without obscure rays. L. 12 ; H. 7 ; 

 W. 4 ; U. f ; An. 135°.— New York and New Jersey. Abundant. 

 Family 19. PSAMMOBIID/E. 



Shell elongated, gaping, with nearly central umbones ; pallial 

 sinus deep ; cardinal teeth two in each valve ; ligament long and 

 prominent 



1. Tagelus, Gray. 



Shell elongated, with subcentrlal umbones ; margins nearly 

 parallel ; ends truncated ; external ligament prominent ; two car- 

 dinal teeth in each valve ; pallial sinus very deep, rounded. 



Animal very large and thick, not entirely retractile within the 

 shell ; mantle closed below ; siphons separated at the ends, united 

 and forming a thick mass at their bases ; incurrent orifice fringed, 

 excurrent plain. 



1. Tagelus gibbus, Speng. Shell thick and solid, oblong, the 

 external ligament on the shorter (posterior) end of the shell ; the 

 anterior end wider ; ends somewhat obliquely truncated ; pallial 

 line distinct, with a very deep sinus ; valves with two awl-shaped 

 teeth, and, behind them, a thick rounded callus to which the 

 ligament is fixed ; lines of growth distinct. Epidermis wrinkled, 

 straw-colored. L. 90 ; H. 30 ; W. 20 ; U. ^.— Cape Cod and south. 

 Common in sand or mud, at about low water mark. 



2. Tagelus divisus, Speng. Shell rather thin and delicate, 

 oblong-oval, the centre curved upward; umbones not promi- 

 nent, central ; hinge with two large teeth in each valve ; surface 

 somewhat wrinkled at the ends, smooth in the centre. Epider- 

 mis yellowish, with a purple band extending fi:om umbo to base. 

 L. 35 ; H. 12 ; W. 9 ; U. i.— Cape Cod and south. Rather com- 

 mon. 



Family 20. TELLINID/E. 

 Shell elongated, nearly or entirely equivalve, with one or two 

 cardinal teeth in each valve ; pallial sinus deep and usually wide ; 

 ligament external, prominent. 



* Compressed shells, width about one third height /. Tellina. 



* Convex shells, width about half height. (A.) 



A. Large shells, over 12 long 2. Maeoma. 



A. Minute, under 6 long 3. Gastranella. 



