1M I'AL.KDSTOLOGY OF NEW YORK. 



Beaks near the anterior end of the valve obtuse, rounded, prominent, 

 inclined forward. Qmbonal 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 i lie righl 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 

 ncarh as far as the posterior margin of the shell. 



Tesl thin, marked by concentric stria 1 of growth, which are crowded into 

 fascicles at irregular intervals, riving 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 stria' 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 'IS mm., height 

 Hi mm., hinge-line in mm. The specimens are usually smaller than those 

 figured. 



This species, in form of body ami in the concentric striae, resembles 

 L. longispinum ; hut the anterior extremity (especially in the right valve) is 

 narrower, the win- i> extended farther down the body of the valve, and the ■ 

 spine i- less produced. 



This shell in it- usual condition of preservation (that is. ha\ ing the spiniform 

 process of the wing broken oil', or the wing partially covered) presents the 

 characters described 1 > x Mr. Conrad, although not illustrated in his figure. A 

 specimen of this species i- Labelled in the hand writing of Mr. Conrad, Avicula 

 protr.rta, and therefore the name is retained. 



