38 PAL.EONTOLOC'Y OF NEW YORK. 



ear. Both species sliow the smooth area on tlie uinlid of tlic lidit \;ilve; a 

 character not observed in any other species liere described. 



Formation and locality. In the Hamilton L'roup; shores of Canandaigua lake, 

 Ontiirio county, N. Y. 



AVICULOPECTEN MUCRGNATUS. 



I'l.ATK III. Fro. 15. 



Am-iiJitpert) 71 mucroniitiix. ITai.i,. Pal. N. V., vol. v, pi. 1. Plait's ami Kxiilanatiim.s : PI. S, ti^;. I.j. 



.Ian., 1S.S8. 



Shell small, i-otiind-ovate, slightly oblique; length a little greater than the 

 height. Basal and anterior margins regularly rounded; posterior margin 

 lull, abruptly sloping to the beak. 



Left valve strongly convex. Right valve not observed. 



Hinge-line straight, ecpial to the greatest length of the shell, extended 

 iintcriorly. 



Beak obtiise-angidar, directed forward, nearly central. Umbo deep, sides 

 subtending an ol)tu.se angle, sloping to the ears. 



Ears sul)-equal. Anterior car narrow-triangular, elongate, acuminate, 

 delined liv the deep byssal sinus anil marked sulcus; margin concave. 

 Posterior ear wider, limited by an undefined sulcus ; margin concave ; 

 extremity acute. 



Test ornamented by rounded i-adii, wliicli bifurcate towards tlii' margin; 

 crossed by prominent, regular, concentric stria'. 



Hinge-area sim|ilc. 



The spei'imcn lias a Iciigtli of Id mm., luught 15 mm., hingf-liuc 111 mm. 



This .species differs from A. insignis, A. bellus and A. ornatus in the liillowing 

 characters: the anterior ear is narrower, the outline of the shell is less 

 oblique, and the form is more rotund. 



Formation and locali 1 1/. In cdcarcous slmlcs of the Hamilton group at Dresden, 

 Yates county, N. Y. 



