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. (Conrad, Ac. Sc. Vol. 6, p. 263, pi. 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. 



Obs. 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. 



Modiola plicattjla. 



PLATE XXIV. FIG. 258. 



(STATE COLLECTION.) 



Modiola plicatula. Lam. An. sans vert. Vol.3, p. 10. Ed. Brux. 



M. semicoslata. Conrad, Jour. Acad. Nat. Sciences, Vol. 7, p. 244, pi. 20, fig. 7. 



M. plicalula. Gould, 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 : a few distant concentric narrow 

 impressed lines crossing the radiating stria. 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, • 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. 



