1S4 PAL2E0NT0L0GY OF NEW YORK. 



Beaks near the anterior ciid nl' the xalvc ()l)tnse, rmimlcil. iiiiiinini'iit, 

 ini'lined lorwainh Uiiihonal reiiioii imiinw, gihhoiis lor a short spaee helow 

 the hiuge, suhtendiug an acute angle. 



Anterior end scarcely anriculate, ahniptly rounded hi the left valve, pointed 

 in the right valve, limited hy a broad, nndelined depression, wliiiji is le.ss 

 marked in the right valve. Byssal sinus shallow. Wing narrow-tiiangular, 

 joining the IkxIv near the posterior extremity ol' the valve, defined hy the 

 direction of the striae; margin deeply conca\e, the greatest concavity just 

 beneath the hinge-line; extremity produceil into a sharp spine which extends 

 nearly as for as the posterior margin of the shell. 



Test thin, marked by concentric stria? of growth, which ;ire crowded into 

 fa.scicles at irreirular intervals, giving a somewhat wrinkled oi- undulatinsr 

 surface. On the anterior side the stria' are crowded and laraellose, while 

 they are quite regular and closely arranged over the wing. On the external 

 shell the stria? ai-e elevated into regular, equidistant lamellfe. 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 uni^nowii. 



The largest specimen observed Ikis a length of 2li iniii.. height \'-\ uini., 

 hinge-line li<l nnn. A similar right valve has a lengtli of I'^i mm., height 

 111 mm., hinge-line hi mm. The specimens are usually smallei- than those 

 figured. 



This species, in form of body and in the cimcentric stria?, resembles 

 L. Inngispinum ; but the anterioi- extremity (especially in tlii' right valve) is 

 narrower, the wing is extended farther down the body of the vahe. ami the 

 spine is less produced. 



This shell in its usual condition of prest'rvation (that is. having the spinilbrm 

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

 characters described by Mr. Conhah. although not illustrated in his figure. A 

 specimen of this species is labelleil in the liami writing of Mr. Conr.vd, Avicula 

 protexta, and therefore the name is retained. 



