4:58 



DESCRIPTIONS OF NEW SPECIES OF FOSSILS FROM THE 



A.P.S, 



iTr7l889i 



■width of the shell ; extremities curving outward, the lateral margins abruptly rounded, 

 and the basal margins broadly rounded ; on the ventral valve slightly constricted at 



the middle. Dorsal valve flattened, greatest convexity a little 

 below the beak, gently sloping to the front and lower lateral 

 margins, more abruptly curving to the cardinal extremities; 

 at the middle of the base a shallow depression, which con- 

 tinues about one-half of the distance to the beak. Ventral 

 valve more convex, greatest convexity about one-third the length from the beak ; 

 beak incurved and projecting beyond the area line. 



Sui-face marked by conspicnous i-adiating strife, which are sometimes of unifoi-m 

 size, but usually near the base there are very fine alternating striiB. The large striae 

 are marked at infrequent intervals by elongate pits or openings. The radiating striae 

 are crossed by fine, indistinct concentric stria?, and at greater intervals by distinct 

 lines or varices of growth. 



On the casts of the interior of the ventral valve the muscular impression is ovate 

 in outline, the length equal to more than two-thirds that of the shell; width two- 

 thirds the length ; bilobed by the callosity of the adductor muscle. The sides are 

 somewhat distinctly lobcd in three divisions. 



This species most closely resembles OrfJiis circulas of this foi'mation, but the 

 valves are incqual, the outline less circular, the greatest width being below the base, 

 and is constricted at the base. The muscular impression is larger. 



Formation and locality. Clinton group, above fossil ore, from McKee's ore bank, 

 seven miles north-west of Lewistown, Miftlin count}' ; also, ore mine north of Black- 

 log creek, Orbisonia, Huntingdon county, Pennsylvania. 



CriONETES PUNCTATA Simpsou, n. sp., Fig. 8. 



Shell semicircular, plano-convex or concavo-convex ; greatest width at about the 

 middle of the shell ; height from two-thirds to three-fourths the width ; length of 







hinge line usually less than the width of 

 the shell, but sometimes equal to it and 

 occasionally greater. The cardinal ex- 



it-' 



tremities are rectangular, or sometimes 

 produced in slight acute extensions, rarely rounded ; lateral and dorsal margins reg- 

 ularly rounded. 



Ventral valve, varying fiom moderately convex to gibbous; greatest convexity 

 at the middle, gently curving to the beak, more rapidly to the latero-basal margins. 



