184 
PALEONTOLOGY OF NEW YORK. 
Beaks near the anterior end of the valve obtuse, rounded, prominent, 
inclined forward. Umbonal region narrow, gibbous for a short space below 
the hinge, subtending an acute angle. 
Anterior end scarcely auriculate, abruptly rounded in the left valve, pointed 
in the right valve, limited by a broad, undefined depression, which is less 
marked in the right valve. Byssal sinus shallow. Wing narrow-triangular, 
joining the body near the posterior extremity of the valve, defined by the 
direction of the striae; margin deeply concave, the greatest concavity just 
beneath the hinge-line; extremity produced into a sharp spine which extends 
nearly as far as the posterior margin of the shell. 
Test thin, marked by concentric striae of growth, which are crowded into 
fascicles at irregular intervals, giving a somewhat wrinkled or undulating 
surface. On the anterior side the striae are crowded and lamellose, while 
they are quite regular and closely arranged over the wing. On the external 
shell the striae are elevated into regular, equidistant lamellae. In the exfoliated 
shell, or partial casts, the surface presents obscure or obsolescent radii which 
appear to belong to the intimate shell-structure, and which are not shown on 
well-preserved specimens. 
Interior unknown. 
The largest specimen observed has a length of 26 mm., height 13 mm., 
hinge-line 20 mm. A similar right valve has a length of 23 mm., height 
1(1 mm., hinge-line 16 mm. The specimens are usually smaller than those 
figured. 
This species, in form of body and in the concentric striae, resembles 
L. longispinum; but the anterior extremity (especially in the right valve) is 
narrower, the wing is extended farther down the body of the valve, and the 
spine is less produced. 
This shell in its usual condition of preservation (that is, having the spiniform 
process of the wing broken off, or the wing partially covered) presents the 
characters described by Mr. Conrad, although not illustrated in his figure. A 
specimen of this species is labelled in the hand writing of Mr. Conrad, Avicula 
protexta, and therefore the name is retained. 
