ITO. TELLINID^. 



Shell equivalve, more or less equilateral, longer than high, 

 with margins closed all around and smooth within. Hinge with 

 two cardinal and one anterior and one posterior lateral teeth in 

 each valve. Left valve with anterior cardinal tooth larger than 

 the posterior, and trigonal in form, but sometimes rather deeply 

 emarginated below, placed directlj'^ under the beak; posterior 

 cardinal tooth small, slender, and ranging obliquely backward 

 and downward close to the larger one, so as to leave only a 

 slender pit between, corresponding to another on the anterior 

 side of the principal cardinal tooth, which two pits are for the 

 reception of the cardinal teeth of the right valve ; anterior and 

 posterior lateral teeth both elongated parallel to the cardinal 

 margin, the former approaching more nearly to the cardinal 

 teeth. Right valve with, under the apex, two diverging, slender, 

 cardinal teeth, like the posterior one of the other valve, with a 

 triangular pit between them for the reception of the princi|al 

 cardinal tooth of the left valve ; anterior one more oblique than 

 the other, and nearly or quite connecting with the lateral tooth 

 on that side ; lateral teeth like those of the left valve ; the 

 anterior one apparently fitting under and the posterior above 

 that of the other valve. Muscular impressions shallow ; pallial 

 impression with a moderate rounded sinus, directed obliquely 

 forward and upward. Ligament unknown, but believed to be 

 external. Surface without ornamentation. 



Strigilla, Turton, 1822. 



Distr. — 11 sp. W. Ind., Panama, Polynesia, etc. Fossil; 

 Tertiary. S.carnaria, Linn, (cxii, 71-73). 



Shell orbicular, somewhat convex ; surface with diverging 

 strise ; no posterior flexure or carina ; right valve with a large 

 bifid cardinal tooth, left valve with a smaller, simple tooth ; two 

 lateral teeth in each valve ; pallial sinus angular, profound. 



Macoma, Leach, 1819. 



Syn. — Rexithaerus, Conr. 



Distr. — 85 sp. World-wide. Fossil ; Tertiary. M. umbonella, 

 Lam. (cxii, 74 j. 



Shell oval or subrotund, convex ; cardinal teeth narrow ; no 

 lateral teeth; pallial impression with a profound sinus. 



Animal with a single branchial lamella on each side. " The 

 branchial apparatus," says Clark, " is curious, and a departure 

 from the Tellina type ; it consists of a single, rather elongated 

 branchial plate on each side, situated towards the posterior half 

 of the animal ; it is fixed to the dorsal range by its base running 

 obliquely, indeed almost vertically, from the dorsal to the ven- 

 tral range, becoming joined to its fellow under the posterior and 

 smaller part of the body by a permanent membrane." The palpi 

 are very large and triangular. 



