462 PALEONTOLOGY OF NEW YORK. 



This species is distinguished by its alate cardinal slope, which is marked by 

 distinct radiating stria). 



Formation and locality. \n the Chemung group, near Philipsburgh, Alleghany 

 comity, N. Y. 



Prothyris exuta, n. sp. 



PLATE XCIV, FIG. 9. 



Shell large, elongate-trapezoidal ; length more than twice the height ; basal 

 margin nearly straight, gently curving toward the posterior extremity. Pos- 

 terior extremity obliquely truncate. Cardinal line more than half the length 

 of the shell. Anterior end regularly reunded, with a fold and constriction 

 just anterior to the umbo, and a slight notch or sinuosity in the margin at 

 the base of the constriction. ' 



Valves depressed-convex in the lower portion, becoming gibbous in the 

 middle and on the umbonal slope. 



Pliice of the beaks occupied by an opening which appears to have existed 

 during the life of the animal. The margin of this aperture is not fractured, 

 but appears to be entire and to have ]>een slightly retlexed. Umbonal slope 

 obtusely sub-angular, extending in a slightly arcuate direction to the post- 

 inferior extremity. 



Surhice marked by fine concentric striae, which are scarcely preserved in 

 the cast. 



Two specimens measure respectively 32 and 34 mm. in length, and 13 and 

 14 mm. in height. 



This species somewhat resembles P. lanceolata, but it is a larger shell, the 

 posterior termination is at the base and not in the middle, as in that species, 

 and the characters of the anterior end are very different. 



The large opening in tlie place of the beaks appears to have existed in the 

 shell during its life-time, and is a very peculiar feature. It may, perhaps, when 

 further collections are studied, necessitate its separation from typical Prothyris. 



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

 Pa. 



