﻿28 TRUNCILLA 



and tile posterior ridi^c are sli£2;litly knobbed; ])ct\vecn the two 

 there is a wide. \vell-im])ressed radial furrow, which is deepest 

 in the male shell ; surface with decidedly sulcate rest marks ; 

 epidermis varying" from straw-colored or tawny to yellow- 

 green, feebly rayed, subshining or somewhat silky ; psendocar- 

 dinals triangidar ; double in the left valve, single or treble in 

 the right ; laterals curved, strong, double in each valve ; muscle 

 scars small, impressed ; nacre bluish-white to straw-color, rare- 

 ly pink. Male shell subtriangular, the deep, radial depression 

 ending in a rather narrow sinus below. Female shell subellip- 

 tical, the marsupial swelling rounded, moderately produced, 

 often darker than the rest of the shell. 



Length (male) 55, height 40, diam. t,t, mm. 



Length (male) 53, height 45, diam. 33 mm. 



Length (female) 58, height 47, diam. 32 mm. 



Length (female) 57, height 43, diam. 33 mm. 



Tennessee and Cumberland River drainage. 



Type locality. Florence and Tuscumbia, Ala. 

 Unio prophiqmis Lea, Pr. Ac. N. Sci. Phila., I, 1857, p. 83 ; Jl. 



Ac. N. Sci. Phila., V, 1862, p. 63, pi. v, fig. 212; Obs., VIIL 



1862, p. 67, pi. V, fig. 212. — Sow^ERBY, Conch. Icon., XVI, 



1868, pi. Lxxix, fig. 417. 

 Margaron (Unio) propinquus Lea, Syn., 1870, p. 34. 

 Trtmcilla propinqna Simpson, Syn., 1900, p. 523. 



Rather more solid and inflated than T. perplexa, with a 

 deeper, narrower radial impression and having a much less de- 

 veloped marsupial swelling in the female shell. It is rather 

 more in equilateral than perplexa. 



Truncilla biemarginata (Lea). 



Shell subtriangular, subrhomboid or irregularly obovate. 

 solid, but little inflated, inequilateral: beaks moderately full 

 and elevated ; posterior ridge decidedly biangulate ; median 

 ridge but moderately developed ; the radial depression between 

 the two wide and shallow ; growth lines strong and irregular r 

 epidermis yellowish-green, faintly rayed; pseud ocardinals tri- 

 angular, two in the left valve and three in the right ; laterals 

 double in the left valve, partly double in the right; nacre 



