Lamellibranchiata. 243 



Formation and localities. In the soft shales of the Hamilton group 

 at Tinker's Falls, Onondaga county; Bellona, Yates county, and near 

 Norton's Landing, Cayuga lake, N. Y. 



AVICULOPECTEN ORNATUS. 



Aviculopecten ornatus, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: 

 PI. 2, figs. 7, 8 ; pi. 3, fig. 14. Jan., 1883. 



Shell small, longitudinally oblique-ovate, sub-rhomboidal; length and 

 width in the proportion of three to four; margins regularly rounded. 

 Valves depressed-convex; left valve somewhat more convex than the 

 right, and a little larger. Hinge-line straight, slightly less than the 

 length of the shell, central with regard to the body of the shell. 

 Beak obtuse-angular, directed forward, situated a little anterior to 

 the middle. Ears sub-equal. Posterior one the larger, triangular 

 flat or concave, defined by the abrupt post cardinal slope of the 

 umbo; extremity acute; margin concave. Anterior ear defined by a 

 deep sulcus ; byssal sinus deep, most strongly marked in the right 

 valve. 



Test of the left valve ornamented by about 25 strong, sharp, 

 elevated rays, and wide interspaces which are marked with a smaller 

 ray; crossed by undulating concentric striae which are curved back- 

 ward between the stronger rays, producing arched fimbriae. The 

 right valve shows the radiating striae originating near the umbo, 

 which is smooth, and increasing by a double bifurcation, giving them 

 a fasciculate appearance; they are crossed by undulating, concentric 

 striae. The ears are marked by strong, radiating lines and fine, 

 concentric striae. 



The length of the largest specimen is 18 mm., height nearly 15 

 mm., and hinge-line about 17 mm. 



This species, in form and general appearance, is very similar to A, 

 iellus ; it differs conspicuously in the ornamentation, with propor- 

 tionally shorter posterior ear. 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 Canan- 

 daigua lake, Ontario county, N. Y. 



Aviculopecten- mucronatus. 



Aviculopecten mucronatus, Hall. Pal. N, Y., vol. v, pt. 1. Plates and Ex- 

 planations : PI. 3, fig. 15. Jan., 1883. 



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

 the height; basal and anterior margins regularly rounded; pos- 



