262 MEMOIRS OF THE CARNEGIE MUSEUM. 



EuRYNiA (Micromya) fabalis (Lea) (1831). 

 Micromya fabalis (Lea) Simpson, 1914, p. 33. 



Plate XVI, figs. 4, 5. 

 Records from Pennsylvania: 



Harn, 1891 (western Pennsylvania). 

 Marshall, 1895 (Allegheny River, Warren Co.). 

 Ortmann, 19096, p. 188.'" 



Characters of the shell: Shell small, but comparatively thick. Outline sub- 

 elliptical to subovate, rather short, generally a little less than twice as long as high. 

 Anterior and posterior ends rounded. Upper and lower margins more or less 

 curved, the lower sometimes nearly straight, or even concave in the middle. Beaks 

 not much elevated above the hinge-Hne. Beak-sculpture fine and rudimentary, 

 consisting of four or five bars, which are double-looped and interrupted in the 

 middle. The posterior loop is represented by a mere tubercle. Valves more or 

 less convex, flattened upon the sides. No distinct posterior ridge. Posterior 

 slope slightly convex. 



Epidermis yellowish, or light or dark green. Generally covered all over with 

 green rays, but the rays may be absent on the anterior section. The rays are 

 not very sharp, and are broader or narrower, but on the posterior section of the 

 shell they are generally rather narrow, and very often more or less vmdulating. 

 On the posterior slope they are indistinct. Old shells often incline to a uniform 

 dark green, brown, or blackish color, with very indistinct rays. Growth-rests 

 obscure. 



Hinge well-developed. Pseudocardinals two in left, one or two in right valves, 

 comparatively heav}^, thick, stumpy, and somewhat crenulated. Interdentum 

 absent or narrow. Laterals moderately long, thick and heavy, especially the one 

 in the right valve, which stands upon a heavy basal plate. Beak-cavity shallow. 

 Dorsal muscle-scars in the beak-cavity. Adductor-scars distinct, and rather 

 deeply impressed, especially the one anterior. Nacre silvery white, sometimes 

 faintly salmon or pinkish toward the beak-cavity; more or less iridiscent posteriorly. 



Sexual differences rather well marked. The male shell is not much swollen, 

 and has a long-ovate outline, with the posterior end narrower and more narrowly 

 rounded than the anterior. The lower margin is generally gently curved. In 

 the female shell, which is generally more inflated, the outline is more subelliptical, 

 and the posterior end more broadly rounded than in the male. This is brought 



'" Rhoad's Unio parvus (1899) from Beaver River, Wampum, Lawrence Co., refers probably to 

 this species. 



