LAMELLIBRANCHIATA. 423 



Beaks sub-central, moderately prominent and incurving over the hinge- 

 line. 



Surface marked by fine, closely arranged, undulating concentric striae, and 

 by from forty to forty-five rounded or somewhat flattened radii, which are 

 frequently duplicating on the anterior and posterior slopes. Interspaces nar- 

 rower than the plications. 



A specimen has a length of 55 mm. and a height of about 42 mm. The 

 original figure given by Mr. Conrad has a length of 65 mm. and a height of 

 51 mm., and is a good representation of the species. 



In form this species more nearly resembles P. Lincklczni than any other, but 

 the plications are much more numerous. It differs from P. potens in its more 

 rotund form and in the duplication and outward curvature of the plications on 

 the anterior portion of the valve. 



Formation and localities. In the coarser shales of the Hamilton group at Caz- 

 enovia, and at Pratt's falls, N. Y. 



Panenka abrupta, n. sp. 



PLATE LXIX, FIG. U ; AND PLATE XCIV, FIG. 16. 



In pai-t CardiolaJ radians (Cohbad), Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. G9, 



tigs. 5-11. 1883. 



Shell of medium size, obovate, broadest below, rapidly tapering above the mid- 

 dle ; length and height nearly equal in the cast. Pallial margin regularly 

 curving from the posterior along the basal margin, and somewhat straighter 

 upon the posterior slope. 



Valves gibbous in the middle and above. 



Ligaraental area distinct with an oblique fold under the beak. 



Beaks sub-central, abruptly attenuate, elevated. 



Surface marked by concentric striaa and by about thirty radii ; those upon 

 the body of the shell being strong, sub-angular and wider than the inter- 

 spaces. The plications sometimes show a tendency to bifurcation and inter- 

 stitial addition. 



