32 NEW YORK STATE MUSEUM 



notable convexity of this right valve and the absence of byssal sinus 

 beneath the anterior wing are features which suggest the subgenus 

 V e r t u m n i a Hall. 



The surface is without any trace of radial marking, but bears fre- 

 quent though rather obscure concentric lines of growth. The species 

 is rare, and the left valve has not been observed. 



Pterinopecten proteus, sp. nov. 



Plate 4, fig. 4-8 



Shell of medium or large size, subcircular in outline with anterior 

 and posterior wings well developed. Left valve normally convex, right 

 valve slightly convex or depressed. Hinge-line straight and making the 

 greatest width of the shell. 



Surface marked by an ornamentation quite variable in its expression. 

 A few stout ribs depart from the beak and maintain their individuality 

 to the margin, becoming broader and somewhat flattened as they extend 

 outward. The intervals between these ribs are broad and in occasional 

 instances are but rarely divided by minor ribs. As a rule, however, 

 these interspaces carry one, rarely two secondary ribs, Avhich are 

 implanted and not produced by dichotomy, and these lesser ribs maintain 

 their minor character throughout, very seldom attaining the size on the 

 margin, of the primary ribs. The mode of increase of these ribs is 

 such that no tendency to their fasciculation is manifested. The variable 

 size and number of the intermediary ribs, however, give each specimen 

 an appearance in this respect unlike all others. The radii are crossed 

 by fine, elevated lamellae, which are moderately and equally distant over 

 the upper and median parts of the shell, but become closely crowded 

 near the margins. These eancellate all radii. On the right valve there 

 is notable variations in the size of the primary ribs, but no ribs which 

 are distinctly intercalary except over the anterior slope. Concentric lines 

 are also present, and these may become lamellae over the peripheral 

 regions, in which case they may obscure the ribs and produce an 

 approximately smooth surface. Specimens of both valves have been 

 observed on which the predominance of the concentric lines almost 

 obliterates the radii, specially on internal casts. This, however, is not 



