178 NEW-YORK FAUNA — MOLLUSCA. 
GENUS NUCULA. Lamarck. 
Animal with its mantle open only on its lower margin, denticulated along the back: buccal 
appendages anterior, long-pointed, stiff and applied against each other. Gills on each side 
and above, narrow and almost as long as the whole animal: foot very large, forming an 
oval disk, with its edges digitated. Shell transverse ; no area for the ligament between 
the beaks: a straight series of teeth on each side, forming an angle at a spoon-shaped 
pit which separates them: ligament partly interior. 
Oss. This genus has been chiefly illustrated in its American species by Messrs Couthouy, 
Gould and Storer. About ten species have been discovered on the coast of the United States. 
Some of them have the power of leaping to a great distance, as we have noticed under the head 
of Pecten concentricus. 
NucuLa THRACIAFORMIS. 
PLATE XII. FIG. 217. a. B. 
Nucula thracieformis. Storer, Bost. Journ. Nat. Hist. Vol. 2, p. 122 (woodcut). 
N. id. Gou.p, Invertebrata of Mass. p. 97, fig. 66. 
Description. Shell large, solid, oblong-ovate, broadest behind, gaping at both ends. An 
oblique prominent fold extends from the beak to the posterior third of the basal margin, form- 
ing a distinct impression within ; another fold, but not so distinct, radiates from the beak, and 
forms an acute angle with the hinge margin: these folds give a peculiar undulating form to 
the posterior surface of the shell. Beaks on the anterior third of the shell, somewhat elevated, 
pointed, inclined backwards, and nearly touching each other ; their internal cavities capacious. 
Teeth very prominent; with about fourteen teeth on each side of the large central cavity or 
pit: these teeth are angular, regular, equidistant, and highest in the middle of each series, 
closely interlocking with those of the other valve. 
Color. Brownish olive, varied with fuscous : beaks reddish brown; within polished white, 
tinged with bluish. 
Length, 1:3. Transverse diameter, 2.1. 
The specimens noticed by Dr. Gould are of larger dimensions than this, which was kindly 
loaned to me by Dr. Jay for description, and which he obtained from the stomach of a cod- 
fish on our coast. Those described by Dr. Storer and Gould were found in the stomachs of 
the P. dentata, or Sand-dab. It is a large and beautifully distinct species. 
