LAMELLIBRANCHIA TA. 
455 
an elongate posterior muscular impression. Anterior muscular impression 
strongly marked. 
Three specimens measure respectively 30, 34 and 38.5 mm. in length, and 
26, 28 and 33 mm. in height. 
This form appears to be only a variety of S. Chemungensis, with a more erect, 
distinctly quadrangular outline, and having a wider post-cardinal slope. 
Formation and localities. In the Chemung group, on Cayuta creek and at 
Factoryville in Tioga county; on the banks of Chemung creek and at Ithaca, 
N. Y. 
SCHIZODUS OBLATUS. 
PLATE LXXV, FIGS. 43, 44. 
Schizodus oblatus, Hall. Prelim. Notice Lamellibranchiata, 2, p. 97. 1870. 
In part Cytherodon (Schizodus ) oblatus , Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 75, 
figs. 41-45. 1883. 
Shell of medium size or larger, broadly sub-elliptical; length one-fourth 
greater than the height; basal margin regularly curving. Post-inferior 
extremity obtusely angular and the margin above sub-truncate. Cardinal 
line less than half the length of the shell. Anterior end broadly rounded. 
Yalves convex in the lower portion, becoming gibbous or ventricose in the 
middle and above, depressed-convex along the middle of the lower portion of 
the valve. 
Beaks a little anterior to the middle, prominent, broad and rounded. 
Umbonal slope obtusely sub-angular, extending to the post-inferior extrem¬ 
ity. 
Surface marked by tine concentric striae, which are but faintly preserved 
in the cast. 
Muscular impressions strongly marked. The posterior scar, on the cardi¬ 
nal slope, is at about the middle of the height of the valve. 
Two specimens measure respectively 30 and 32 mm. in length, and 22 and 
24.5 mm. in height. 
This form differs from any other of the genus, here noticed, in the prominent 
