184 NEW-YORK FAUNA — MOLLUSCA. 
striate every where with longitudinal elevated lines, which are bifid and sometimes trifid towards 
the tip. Color, dark fuscous with purpurescent, with a whitish margin. Length, 1-2; breadth, 
0:8. Southern coast. 
M. leucopheatus. (Conrap, Ac. Sc. Vol. 6, p. 263, pl. 11, fig. 13.) Shell incurved, with a very 
rugose epidermis; anterior side much depressed. Hinge-margin excavated, with the teeth obsolete; 
on the posterior side, under the beaks, is a pointed lamellar tooth, directed inwards. Southern coast. 
GENUS MODIOLA. Lamarck. 
Animal resembling in every respect those of the preceding genus. Shell oblique, wedge- 
shaped. Beaks very near the anterior end, but not terminal. 
Oss. If we admit the zoological principle, that animals of the same organization should be 
classed in the same genus, it would be difficult to say why this genus should be allowed to 
remain. The only constant external character is supposed to lie in the beaks; and yet we 
are assured by high conchological authority, that if a large number of species of Mytilus and 
Modiola are examined, we shall find the beaks so gradually passing from subterminal to 
terminal, that it is impossible to define the limits between the two genera. As, however, the 
division affords some assistance in determining the numerous species, and is adopted by many 
eminent conchologists, we shall follow their arrangement. 
MopiIoLa PLICATULA. 
PLATE XXIV. FIG. 258. 
(STATE COLLECTION.) 
Modiola plicatula, Lam. An. sans vert. Vol. 3, p. 10. Ed. Brux. 
M. semicostata. Conran, Jour. Acad. Nat. Sciences, Vol. 7, p. 244, pl. 20, fig. 7. 
M. plicatula, Gouxp, Invertebrata of Mass, p. 125, fig. 81. 
Description. Shell oblong, obliquely dilated, somewhat falciform. Surface with approxi- 
mated deep furrows, radiating towards the dilated margin, fainter on the basal margin, but 
more distinct near the beaks, which are smooth, often eroded: afew distant concentric narrow 
impressed lines crossing the radiating strie. Beaks prominent, rounded: hinge-margin 
straight, ascending ; basal margin concave, depressed, with a small fissure for the exit of the 
byssus. 
Color. Epidermis greenish yellow, occasionally reddish brown; within pearly, with faint 
purplish tints. 
Length, 0°8-—1°5. Width, 2°4-4°5. 
This is common every where along the coast, on salt-marshes, and along the margins of 
creeks and other tide estuaries. When decorticated, the interior often exhibits a brilliant 
nacre, 
