278 
PALEONTOLOGY OF NEW YORK. 
elongate form, more regularly convex umbonal slope, more regularly rounded 
posterior extremity, and narrower anterior end. 
This is probably the species described by Mr. Conrad as Cypricardites myti- 
loides, of which he gives the following description: 
“ C. mytiloides. Ovate, slightly ventricose; lines of growth prominent; umbo 
prominent; dorsal margin elevated; anterior basal margin very oblique and 
slightly contracted; posterior side profoundly dilated and the margins regularly 
rounded. Locality. Near Ogden’s Ferry, tab. of form. No. 23.” 
Formation and localities. In the shales of the Hamilton group; principally in 
the eastern and central portion of the State, on the shores of Seneca and 
Cayuga lakes. 
MODIOMORPHA ALTA. 
PLATE XXXVII, FIGS 1, 2 (4, 5, 6?), 7-12, 15, 16; AND PLATE LXXX, FIG. 7. 
Cypricardites aJta, Conrad. Geol. Surv. N. Y., Ann. Rep., p. 52. 1841. 
Modiomorpha alta, (Conrad) Hall. Prelim. Notice Lamellibranchiata, 2, p. 75. 1870. 
“ “ “ “ Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 37, figs. 1-16 ; 
pi. 80, fig. 7. 1883. 
Shell larger than the medium size, broad, rhomboid-ovate; length one-third 
greater than the height; the basal margin for two-thirds of its length from 
the anterior curve is nearly straight, varying from slightly concave to nearly 
straight, abruptly curving at the post-basal extremity, and continuing to the 
post-cardinal margin in an oblique, gently curved outline. In some examples 
the posterior margin is regularly curved, cardinal margin sometimes form¬ 
ing a nearly straight line, usually gently arcuate. Anterior end produced 
beyond the beak from one-sixth to one-fourth the length of the shell, 
obliquely truncated, obtuse, rounded below; its greatest extension is below 
the middle of the shell. 
Valves convex, gibbous on the umbonal and medial portions of the 
shell; the umbonal ridge is gibbous and arched upward; the point of 
greatest convexity is about the middle of the shell or a little posterior. 
The depth of both valves is equal to two-thirds of the height of the shell. 
Hinge-line straight, oblique, extending for less than half the length of 
the shell. 
