214 MEMOIRS OF THE CARNEGIE MUSEUM. 



Obliquaria reflexa Rafinesque (1820). 

 Ohliquaria reflexa Rafinesque, Simpson, 1914, p. 330. 



Plate XIII, fig. 4. 

 Records from Pennsylvania: 



Clapp, 1S95 (Allegheny Co.). 



Rhoads, 1899 (Oliio River, Coraopolis, Allegheny Co., and Beaver, Beaver Co.). 



Ortmann, 19096, p. 193. 



Characters of the shell: Shell rather small, hardly of medium size, thick and 

 solid. Outline more or less rounded, subovate or subtrapezoidal, short and high, 

 more or less pointed ' at the lower posterior end. Anterior and lower margins 

 regularly rounded; lower margin ascending posteriorly, straight or slightly con- 

 cave. Upper margin short, passing in a curve or blunt angle into the obliquely 

 descending posterior margin. Beaks near, but somewhat in front of the middle, 

 elevated over the hinge-line and incurved. Beak-sculpture consisting of a few 

 (two to three) rather heay>% but not sharply defined, concentric bars, which have 

 an indistinct tubercle upon the posterior ridge. Valves fiat or convex, with a 

 more or less distinct, rounded posterior ridge, generally with a shallow radial 

 furrow, which may be obsolete. In front of this furrow stands a row of large, 

 prominent knobs, which alternate with each other on the opposite valves. They 

 are rounded, conical, or vertically compressed. Maximum number of these knobs 

 on each valve, four or five. Posterior slope often ornamented with short, corru- 

 gated ridges. 



Epidermis yellowish to brown, with indistinct darker concentric bands. 

 There may be raj's, fine, wavy, or broader; they sometimes spread over the surface, 

 so that the whole epidermis appears dark green. In old specimens the epidermis 

 is often uniformly brown. 



Hinge weU-developed. Pseudocardinals large, ragged, triangular, two in the 

 left, one in the right valve. Laterals thick and short. Interdentum short and 

 rather narrow. Beak cavity moderate. Dorsal muscle-scars in the beak-cavity. 

 Anterior adductor-scars small, deeply impressed, posterior ones also small and 

 distinct, but less impressed. Nacre silvery white, very rarely colored: I have 

 seen only a few individuals from Alabama with purple nacre. 



Sexual differences in the shell very uncertain. On the average, the females 

 are more swollen, with the radial furrow indistinct, and the posterior lower margin 

 not emarginate; while the male shells are more compressed, with the furrow more 

 distinct, and the emargination of the lower margin more frequently developed. 

 These differences, however, are slight, and there are shells in which the sex cannot 



