492 PALEONTOLOGY OF NEW YORK. 



PRORHYNCHUS, n. g. 



Prorhynchus quadratom. 



PLATE LXXIX, FIGS. «M9 ; ANl> PLATE XCVI, FIG. 6. 



Palcuinatina quadrata (Hall). 8. A. Millkr. Cat. Am. Pal. Foss., p. 199. 1877. 



" " Hall. Pal. N. Y.. vol. v, pt. 1. Plates and Explanations : PI. 79. tig«. 40-49. 1883. 



Shell large, inequivalve, quadrate, sub-rhomboid ; 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 flat. 



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 striae, the impressions of which are left 

 on the cast of the interior. 



The cast shoAvs some striae 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, 

 and 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. 



