﻿TRUNCILLA 29 



bluish-white to creamy. Male shell with a decidedly biangu- 

 late posterior ridge ending in a biangiilation below, the radial 

 depression in front of it wide ; female shell somewhat obovate, 

 the radical depression fading out on the rounded, darkened 

 marsupial swelling. 



Length (male) 46, height 32, diam. 22 mm. 



Length (female) 36, height 28, diam. 17 mm. 



Tennessee River drainage. 



Type locality, Florence, Ala. 

 Unio biemarginatus Lea, Pr. Ac. N, Sci. Phila., l, 1857, p. S3 ; 



Jl. Ac. N. Sci. Phila., VL 1866, p. 47, pi. xvi, fig. 45 ; Obs., 



XI, 1867, P- 5L pl. XVI, fig. 45. 

 Margaron (Unio) biemarginatus Lka, Syn., 1870, p. 38. 

 Trimcilla bieniarginata Simpson, Syn., 1900, p. 524. 



Smaller than T. perplexa or T. propinqua, having the pos- 

 terior ridge more decidedly biangulate. 



Truncilla CAPS.^iFQRMis (Lea). 



Shell subsolid, elliptical or irregularly obovate, convex, 

 somewhat inequilateral ; beaks moderately full and elevated, 

 their sculpture very feeble ; surface with irregular growth lines ; 

 epidermis yellowish-green with green, rather faint rays ; pseu- 

 docardinals small, subcompressed, double in each valve; lat- 

 erals single in the right valve, double in the left ; anterior scars 

 small, impressed ; posterior scars large, shallow ; nacre bluish- 

 white to creamy, thicker in front. Male shell almost evenly 

 elliptical, often with a double posterior ridge and slightly bi- 

 angulate behind. Female shell with an enormously developed, 

 rounded, compressed marsupial swelling, which is occasionally 

 toothed a little and is dark green in color and thin. It is fre- 

 quently marked off from the rest of the shell by a sulcus in 

 front and behind. 



Length (male) 67, height 42, diam. 26 mm. 



Length (female) 48, height 36, diam. 17 mm. 



Length (female) 52, height 2,7, diam. 19 mm. 



Tennessee River drainage. 



Type locality, Cumberland River. 



