282 
PALAEONTOLOGY OF NEW YORE 
Modiomokpha cymbula. 
PLATE XXXVI, FIGS. 19, 20. 
Modiomorpha cymbula, Hall. Prelim. Notice Lamellibranchiata, 2, p. 75. 1870. 
“ “ “ Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 36, figs. 19, 20. 
1883. 
Shell of medium size, elongate, sub-elliptical; length a little more than twice 
the height; basal margin regularly convex, acutely rounded at both extrem¬ 
ities ; cardinal line -regularly curving from the beaks to the posterior 
extremity. Anterior end narrow, sub-nasute, without special limitation. 
Yalves moderately and regularly convex, the greatest convexity being 
about the middle of the length. 
Hinge-line oblique, curving; length a little less than half the length of the 
shell. 
Beaks sub-anterior, small, narrow, acute, closely appressed. Umbonal 
region moderately convex, without any defined ridge, but the prominence 
extends parallel to the cardinal line for more than two-thirds the length of 
the shell. The anterior side of the umbonal region is flattened or depressed 
in the cast, the depression extending downward nearly to the base, but not 
affecting the margin. 
Test comparatively thick ; surface markings not preserved. The anterior 
muscular impression is strong and large, with a small and deep retractor 
scar. Pallial line parallel with the basal margin, abruptly recurving at the 
posterior end and terminating in a large, shallow posterior adductor 
impression. 
The specimen has a length of 60 mm., and a height of 28 mm. 
This form is more elliptical than any of the preceding species of the 
Hamilton group, but is not so symmetrically elliptical as M. regularis and 
M. linguiformis of the Helderberg limestone. It is distinguished from all the 
species of the genus by its narrow and acute anterior and posterior extremities. 
The species is of extremely rare occurrence, a single specimen only having 
been observed in all the collections. 
