390 



NORTH AMERICAN INDEX FOSSILS. 



49. P. hero Hall. (Fig. 497, d.) Devonic. 



Distinguished by small size, small, subcentral beaks, and strong, 

 distant radii. 



Marcellus shale : New York. 



Fig. 497. a, p, Panenka ventricosa, left valve and cardinal view showing triangular area 

 under the beak ; c, P. potens, right valve ; d, P. hero, left valve. (N. Y. Surv. ) 



50. P. costata Hall. (Fig. 498, b.) Devonic. 



Differs from P. hero in the broader, more rounded radii and in 

 its larger size. 



Marcellus shale : New York. 



51. P. potens Hall. (Fig. 497, c.) 



Large; radii rounded, numbering 35 to 40. 

 Hamilton : New York. 



Devonic. 



