170 TELLINIDA. 
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 directly 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.—1% sp. W. Ind., Panama, Polynesia, etc. Fossil; 
Tertiary. S.carnaria, Linn. (exii, 71-73). 
Shell orbicular, somewhat convex; surface with diverging 
strie ; 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.—Rexitherus, Conr. 
Distr.—85 sp. World-wide. Fossil; Tertiary. J. umbonella, 
Lam. (exii, 74). 
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 bya permanent membrane.” The palpi 
are very large and triangular. 
