LAMELLIBRANCHIATA. 493 



Prorhynchos nasutum, n. sp. 



PLATE XCVI, FIG. 6. 



Shell of medium size, sub-rhomboid-obovate ; length more than one-third 

 greater than the height; basal margin nearly straight, curving upward in 

 front. Posterior extremity almost vertically truncate. Cardinal line straight. 

 Anterior end nasute above, rounded below. 



Left valve depressed-convex in the lower part, gibbous in the upper and 

 umbonal regions. Right valve depressed-convex, scarcely gibbous above. 



Beaks anterior to the middle, appressed, incurved, scarcely elevated above 

 the hinge-line in the left valve. In the left valve there is a broad undefined 

 depression, extending vertically from the umbo to the base. Umbonal slope 

 obtusely angular and broad in the left valve, less conspicuous in the right, 

 extending to the post-inferior angle. Post-cardinal slope broad, limited by 

 a shallow longitudinal depression just above the umbonal ridge. 



Surface marked by fine concentric striae, which are sometimes fasciculate. 



A specimen has a length of 25 mm. and a height of 18 mm., the length, 

 including the nasute anterior extension, is 29 mm. 



This species is distinguished from the preceding by its proportionally greater 

 height, more nearly central beaks, broad umbonal ridge, the nasute anterior 

 extremity and the greater convexity of the right valve. 



Formation and locality. In the upper part of the Chemung group, at Warren, 

 Pa. 



Proriiynchus angulatum, n. sp. 



PLATE XCVI, FIG. 7. 



Shell large, sub-rhomboidal ; length and height as five to three ; basal margin 

 nearly straight, oblique to the hinge-line. Posterior extremity obliquely 

 truncate, slightly sinuate in the middle. Cardinal line elongate, straight. 

 Anterior end long, narrow, produced above, angular at the extremity and 

 retrally truncate below, to the antero-basal angle. 

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