236 NEW-YORK FAUNA — MOLLUSCA, 
GENUS COCHLODESMA. Couthouy. 
Animal with a thin mantle, closed by a membrane in front, except at the antero-inferior 
extremity, where it gives passage to a broad compressed foot extending along the whole 
inferior surface of the abdominal mass. Edges of the pallium thickened, and a little rugose. 
Siphons long, narrow and divided in their whole extent, and opening separately into the 
branchial cavity. Shell thin, fragile, inequivalve, inequilateral ; right valve most convex. 
Beaks moderately prominent, cloven; ligament double. Hinge a spoon-shaped process in 
each valve, supported by one or more oblique ribs. Palleal impression deeply indented 
behind. ° 
CocHLODESMA LEANA. 
PLATE XXXI. FIGS. 299, 301. a. B. 
(STATE COLLECTION.) 
Anatina leana, Conrab, Jour. Acad. Nat. Sc. Vol. 6, p. 263, pl. 11, fig. 11. 
A. id. RussEt, Essex Jour. Nat. Hist. Vol. 1, p. 52. 
Cochlodesma leana. CouTuHovy, Bost. Jour. Nat. Hist. Vol. 2, p. 170. 
Cc. id. GouLp, Invertebataof Mass. p. 49, figs. 27, 30. 
Description. Shell very thin and fragile, ovate, subcompressed ; the left valve almost flat, 
rounded at both ends; the right valve convex, and subtruncate at the shorter end, slightly 
gaping at both ends. Beaks small, slightly cleft at one side: from the beaks proceeds a ridge, 
more or less obvious to the posterior end. Surface wrinkled, with a yellowish shining epi- 
dermis extending sowewhat beyond the margins ; the spoon-shaped process in the hinge nearly 
horizontal, and resting on an oblique rib directed backwards: no ossiculum. 
Color, white beneath the epidermis. 
Vertical axis, 0°9; transverse ditto, 1°3. 
This is found occasionally along our coast, and is said to be very abundant about Cape 
Cod. The flattened valve is frequently eroded in the centre. 
GENUS THRACIA. Leach. 
Animal resembling Anatina. Shell usually thin, transversely oval, inequivalve ; right valve 
most convex, slightly gaping at both ends. Beaks well marked, and inclined a little back- 
wards. Tooth represented on each valve bya more or less prominent spoon-shaped process. 
Occasionally a cylindrical and semicircular ossiculum is attached to the posterior extremity 
of the internal ligament. Palleal impression deeply excavated behind. 
Oss. This genus was first established by Leach, and has been subsequently more amply 
developed by Deshayes, and also by Mr. Couthouy in his elaborate monograph of the Family 
Osteodesmacea already cited above. 
