238 PALEONTOLOGY OF NEW YORK. 



All the specimens of this species are casts of the interior, with the single 

 exception of an individual which preserves the test very imperfectly. The 

 concentric undulations of the cast are often a conspicuous feature, and the 

 umbonal slope is occasionally obtusely subangular. The wing follows the 

 general contour and convexity of the valve. 



Formation and localities. In the Upper Chemung group, associated witli 

 Spirifera Verneuili near Olean, Alleghany county ; in the vicinity of East Ran- 

 dolpli, and other places in Cattaraugus county, N. Y. 



Pteronites rostratus. 



PLATE XXII, FIG. 21. 

 Pteronites rostratus, Ham,. Pal. N. V., \ol. v, jit. 1. Plates and Explanations : PI. 22, fig. 24. Jan., 1883. 



Shell of medium size, broadly semi-ovate ; body oblique at an angle of about 

 45" to the hinge-line ; length nearly twice the height ; ante-byssal margin 

 oblique, gently curving into the broadly rounded basal margin; posterior 

 margin somewhat obliquely truncate. 



Left valve depressed-convex below, convex in the middle, and somewhat 

 gibbous above. Right valve unknown. 



Hinge-line straight ; length greater than the greatest length of the shell. 



Beak sub-anterior, sub-acute, prominent. Umbonal region moderately 

 gibbous, subtending an acute angle. 



Anterior end nasute. Wing not defined, in direct continuation of the 

 convexity of the body, extending to the posterior extremity ; margin very 

 slightly concave, oblique to the cardinal line, slightly produced at the 

 extremity. 



Test ornamented by fine, elevated, concentric strise, which are continued 

 over the body and wing without interruption, becoming crowded and some- 

 what fasciculate on the anterior side and on the nasute extension in front. 



The umbonal region shows a few concentric imihilations, which are not 

 continued to the middle of the length of the valve. 



