218 MEMOIRS OF THE CARNEGIE MUSEUM. 



Cyprogenia stegaria (Rafinesque) (1820). 

 Cyprogenia irrorata (Lea) Simpson, 1914, p. 326; Cyprogenia stegaria (Rafinesque) 

 Vanatta, 1915, p. 554. 



Plate XIII, iig. 5. 

 Records from Pennsylvania: 



Rhoads, 1899 (Ohio River, Beaver, Beaver Co.) 

 Ortmann, 19096, p. 193. 



Characters of the shell: Shell hardly of medium size, but solid. Outline sub- 

 circular, subtrapezoidal, or rounded triangular. Anterior and lower margins more 

 or less rounded, but the latter tending in the posterior part to be straight or slightly 

 concave. Upper margin short, slightly convex, forming a more or less distinct 

 angle with the posterior margin, which is nearly vertical. Beaks slightly anterior 

 to the middle, moderately inflated and elevated. Beak-sculpture rudimentary, 

 consisting of a few slightly double-looped bars. Valves more or less convex, 

 sometimes making the shell subglobular. Young specimens have a distinct, but 

 rounded, posterior ridge, which becomes effaced in old ones. Generally there is a 

 slight radial groove in front of the ridge, almost effaced in old specimens. Surface 

 adorned b}' flat nodules, most distinct upon the posterior ridge and in front of the 

 groove. Anterior part of the shell smooth, but there may be nodules in the groove 

 and upon the posterior slope, where they may assume a radial arrangement. In 

 old shells the nodules are much obliterated. The gTowth-rests are often marked 

 by concentric, low ridges. 



Epidermis light gTeen or yellow, to light brown, ornamented with green 

 mottlings, which fall into finer or broader, interrupted rays. The broad rays 

 prevail upon the anterior part of the shell, the fine ones upon the posterior. In 

 old shells the mottlings become indistinct. Concentric color-markings are absent 

 or very faint. 



Hinge well-developed. Pseudocardinals heay>', triangular, blunt and ragged, 

 two in left, one in the right valve. Interdentum very broad and short. Laterals 

 rather short, heay>'. Beak-cavity moderately deep. Dorsal muscle-scars in the 

 beak-cavity, upon the hinge-plate. Adductor-scars distinct, small, deeply im- 

 pressed. Nacre silvery white, verj^ rarely with a faint blush of pink. 



I cannot see any sexual differences in the shell. 



L. H. D. 



Size: 1. Godfrey, Cat. No. G1.4760 62 mm. 57 mm. 38 mm. 



2. do. Cat. No. 61.3581 56 " 54 " 34 " 



3. Industry, Cat. No. 61.4422 54 " 52 " 33 " 



I have not seen any larger specimens than No. 1. 



