38 PALEONTOLOGY OF NEW YORK. 



car. Both species show the smooth area on the umbo of the right valve; a 

 character not observed in any other species here described. 



Formation and locality. In the Hamilton group; shores of Canandaigua lake, 

 Ontario county, N. Y. 



AviCULOPECTEX MITROXATUS. 



PLATE III, FIG. 15 



Aviriilnpi rti n muCTonatus, Hall. Pal. N. Y.. vol. v. ]>t. 1. Platt-s and Explanations: PI. 3, tig. 15. 



Jan.. 1883. 



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

 height. Basal and anterior margins regularly rounded ; posterior margin 

 full, abruptly sloping to the beak. 



Left valve strongly convex. Right valve not observed. 



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

 anteriorly. 



Beak obtuse-angular, directed forward, nearly central. Umbo deep, sides 

 subtending an obtuse angle, sloping to the ears. 



Ears sub-equal. Anterior ear narrow-triangular, elongate, acuminate, 

 defined by the deep byssal sinus and marked sulcus; margin concave. 

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

 extremity acute. 



Test ornamented by rounded radii, which bifurcate towards the margin; 

 crossed by prominent, regular, concentric striae. 



Binge-area simple. 



The specimen has a length of 16 mm., height 1"> mm., hinge-line 16 mm. 



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

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

 oblique, and the form is more rotund. 



Formation and locality. In calcareous shales of the Hamilton group at Dresden. 

 Yates county, N. Y. 



