LAMELLIBRANCHIATA. 337 



Valves regularly convex below, gibbous above and in the umbonal region. 



Beaks at less than the anterior third from the end, moderately elevated 

 above the hinge-line. Umbonal slope flattened, giving a slight angularity to 

 the shell above and below it, and an oblique truncation to the posterior 

 extremity. 



Test thick, marked in the anterior portion by fine, regular concentric 

 striae, some of which become elevated into sharp, lamelliform striae, with 

 finer intermediate ones on the posterior half of the shell. The characters of 

 the interior are well shown in figs. 19, 20, 21 and 22 of plate xlix. 



Three specimens measure respectively 35, 38 and 43 mm. in length, and 

 18, 21 and 24 mm. in height. 



This species differs little in size and form from P. muta, but is distinguished 

 by the fine striae on the anterior portion of the shell, and the finer and more 

 subdued character of the lamellose striae on the posterior part. 



Formation and localities. In the soft shales of the Hamilton group, on the 

 shores of Cayuga, Seneca and Canandaigua lakes ; at Darien, in Genesee county, 

 at York and Moscow, in Livingston county, N. Y. ; also in Hardy county, Va. 



Pal^oneilo muta. 



PLATE XLIX, FIGS. 25-32. 



PcHOBimeilo muta, Hall. Prelim. Notice Lainellibranchiata, 2, p. 8. 1S70. 



•< " " Pal. N. Y., vol. V, pt. 1. Plates and Explanations : PI. 49, figs. 25-32. 



Shell large, elongate-ovate ; length less than twice the height. General form 

 and convexity similar to the preceding. 



Entire surface marked by regular, strong, lamellose elevated striae, with 

 very fine, intermediate .striae. 



Three specimens measure respectively 43, 41 and 35 mm. in length, and 

 24, 21 and 20 mm. in height. 



This species has the form and proportions ot P.fecmda, differing principally 

 in the character of the surface, which is entirely covered by strong, lamellose 



