492 
PALAEONTOLOGY OF NEW YORK. 
PRORHYNCHUS, n. g. 
Prorhynchus quadratum. 
PLATE LXXIX, FIGS. 40-49 ; AND PLATE XCVI, FIG. 5. 
Palceanatina quadrata (Hall), S. A. Miller. Cat. Am. Pal. Foss., p. 199. 1877. 
“ “ Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 79. fig's. 40-49. 18S3. 
Shell large, inequivalve, quadrate, sub-rliomboid; length usually more than 
one-third greater than the height; basal margin straight or gently rounded, 
curving upward in front. Posterior extremity almost vertically truncate. 
Cardinal line straight. Anterior end produced above, sub-nasute, obliquely 
truncate or gently rounded below. 
Left valve depressed-convex below, becoming gibbous in the middle, and 
especially in the umbonal region. Right valve depressed-convex, almost Hat. 
Beaks at about the anterior third, appressed, rising but little above the 
hinge. Umbonal slope of the left valve obtusely angular, somewhat arcuate, 
extending to the post-inferior angle. Post-cardinal slope broad, marked by 
an obscure fold below the middle of its length. 
Surface marked by fine concentric strise, the impressions of which are left 
on the cast of the interior. 
The cast shows some strise or grooves on the posterior portion of the car¬ 
dinal line ; anterior to the beaks there is a groove along the hinge, and a 
distinct narrow, divergent furrow, extending from the beak half way to the 
anterior margin. 
Four left valves measure respectively 19, 21, 38 and 45 mm. in length, 
find 12, 15, 22 and 28 mm. in height. Three right valves measure respect¬ 
ively 22, 24 and 32 mm. in length, and 13, 13.5 and 17 mm. in height. 
This shell is remarkable for its sub-quadrate, rhomboidal form, long straight 
hinge-line and the angular or sub-nasute anterior extremity. 
Formation and locality. In a coarse sandstone in the upper part of the Che¬ 
mung group, south of Smethport, Pa. 
