430 PALjEONTOLOGY OF NEW YORK. 



more than half the length of the shell. Anterior end short, declining from 

 the beaks and regularly rounded in front. 



Valves regularly convex below, gibbous in the middle and upper portion. 



Beaks at about the anterior third, prominent, directed forward and 

 incurved. Post-umbonal slope gibbous, defined and extending to the post- 

 inferior extremity. 



Surface marked by numerous fine radii, which are somewhat stronger on 

 the anterior end, and by fine concentric striae. 



Anterior muscular impression well-marked, situated just below the lunule. 



Three specimens measure respectively 22, 24 and 25 mm. in length, and 

 15, 15 and 16 mm. in height. 



This species somewhat resembles P. Sao, but it has a smaller shell, with much 

 finer and more numerous radii, which are direct, and not arched as in that 

 species. 



Formation and locality. In the sandstone of the Chemung group near Sala- 

 manca, N. Y., and at Alleghany springs, Warren county, Pa. 



Pararca Sao, 



PLATE LXX, FIG. 17. 

 Cardiola Sao, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 70, fig. 17. 1883. 



Shell large, broadly elliptical ; length less than one-third greater than the 

 height ; basal margin regularly curving. Posterior extremity obliquely sub- 

 truncate. Cardinal line slightly arcuate. Anterior end short and regularly 

 rounded below the lunule. 



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

 umbonal region. 



Beaks sub-anterior, moderately prominent, incurved. Umbonal slope con- 

 vex, not strongly defined, extending in an arching direction to the post- 

 basal extremity. 



Surface marked by numerous strong, rounded plications. Those on the 

 antero-basal margin are much stronger than those on the posterior half of 



