292 
PALAEONTOLOGY OF NEW YORK. 
become lamellose. Anterior muscular impression shallow, situated just 
within the anterior margin. 
The specimen described has a length of 50 mm., and a height of 27 mm. 
This species bears some resemblance to M. mytiloides, but the beak and 
umbonal region are much less prominent, the anterior end is broader and the 
body of the shell does not expand so rapidly toward the posterior end, mak¬ 
ing the liinge-line less oblique. 
Formation and locality. In the Chemung group, Mansfield, Tioga county, Pa. 
Modiomorpha hyalea. 
PLATE XLI, FIGS. '2S-30. 
Modiomorpha hyalea, Hall. Prelim. Notice Lamellibranchiata, 2, p. 79. 1870. 
“ “ “ Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 41, figs. 28-30. 1883. 
“ ? “ “ Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 40, figs. 5-11 (errone¬ 
ous reference). 18S3. 
Shell larger than the medium size, sub-elliptical; length nearly twice the 
height; basal margin nearly straight, or slightly arcuate near the middle, 
recurving somewhat abruptly at the extremities. Posterior end abruptly 
rounded, obliquely sub-truncate above, and curving into the cardinal line. 
Cardinal margin nearly straight, and parallel to the basal margin of the 
shell. Anterior end gently declining from the beaks, produced, and abruptly 
rounded below; not limited. 
Valves moderately convex in the lower and posterior part, becoming more 
convex and scarcely gibbous in the umbonal region. 
Hinge-line straight, less than half the length of the shell. 
Beaks broad, moderately prominent, curving over the hinge-line, situated 
a little less than one-third the length from the anterior end. Umbonal 
region prominent, scarcely gibbous; the ridge prominent and rounded but 
not gibbous. 
Test thin, marked by closely arranged concentric striae, with occasional 
stronger undulations which are more frequent on the umbonal region. Mus¬ 
cular impressions unknown. Surface of the cast for some distance within 
