444 PALAEONTOLOGY OF NEW YORK. 



This species has the size and form of P. elliptica, but differs in its more prom- 

 inent beaks and more regular concentric strite. 



Formation and localities. In the Chemung group at Mansfield, Pa., and doubt- 

 fully at Philipsburgh, N. Y. 



Paracyclas ignota. 



PLATE LXJOI, FIG. 34. 

 Paracyclas ignota. Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 72, fig. 34. 1883. 



Shell large, obliquely sub-circular, or very broadly sub-ovate ; margins regu- 

 larly curved, slightly produced in front. 



Valves of moderate convexity. 



Beaks sub-central, somewhat prominent, rising a little above the hinge- 

 line. Umbonal depression obscure. 



Surface, in the cast, marked by fine concentric striae, which have been 

 somewhat fasciculate. 



The specimen described has a length of 41 mm. and a height of 38 mm. 



This species diflfers from P. Chemungensis in being a larger form, with less 

 prominent beaks, and with the shell more extended in the upper part. It also 

 differs from P. rotunda in its less prominent beaks, less marked umbonal furrow, 

 and in the upper anterior extension and obliquity of the body of the shell. 



Formation and locality. In the Chemung group, Metidville, Pa. ^ 



Paeacyclas rotunda. 



PLATE LXUI, FIGS. 18, 19 ; and PLATE XCV, FIG. 21. 



In part Carditnuorplia rciunda. Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 63, 



figs. 17-20. 1883. 



Shell large, sub-orbicular, or very broadly sub-ovate ; length a little greater 

 than the height. Anterior and basal margins regularly curving. Posterior 

 end sub-truncate. 



Valves regularly convex below, becoming gibbous in the middle and above. 



