462 
PALAEONTOLOGY OF NEW YORK. 
This species is distinguished by its alate cardinal slope, which is marked by 
distinct radiating strirn. 
Formation and locality. In the Chemung group, near Philipsburgh, Alleghany 
county, N. Y. 
PllOTHYRIS EXUTA, 11. Sp. 
PLATE XCIV, PIG. 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 rounded, 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. 
Yalves depressed-convex in the lower portion, becoming gibbous in the 
middle and on the umbonal slope. 
Place 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 been slightly reflexed. Umbonal slope 
obtusely sub-angular, extending in a slightly arcuate direction to the post¬ 
inferior extremity. 
Surface 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 the 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. 
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