Ill 



smooth, forming a very obtuse angle with the cardinals ; anterior adductor cicatrices 

 distinct, deep, that of the protractor pedis very small ; posterior adductor cicatrix 

 scarcely evident, confluent; pallial line distinct for the anterior two-thirds ; dorsal 

 cicatrices irregularly grouped in the rather large cavity of the beaks, minute; 

 nacre white, iridescent posteriorly. 



Length. Height. Width. 



No. 1. 42.00 mm. 26.00 mm. 23.00 mm. Female. 



No. 2. 36.30 mm. 27.57 mm. 19.25 mm. Female. 



No. 3. «-36. 10 mm. 18.00 mm. 14.60 mm. Male. 



Unio texasensis Lea. 



Proc. Acad. Nat. Sci. Phila, Vol. ix, p. 84, 1857 ; Jour. Acad. Nat. Sci. 

 Phila., Vol. iv, pp. 357, 359, 362, PI. Ixi, Fig. 184, 1860; Observations on the 

 Genus Unio, Vol. viii, p. 39, PL Ixi. Fig. 184 (PI. v. Figs. 38-40). Dewitt 

 Co., Texas. » 



Unio bairdianus 'Lea. Proc. Acad. Nat. Sci. Phila., Vol. ix, p. 102, 1857; 

 Jour. Acad. Nat. Sci., Vol. iv, pp. 360, 361, PI. Ixi, Fig. 186, 1860; Observa- 

 tions on the Genus Unio, Vol. viii, p. 42, PI. Ixi, Fig. 186 (PI. vi. Figs. 41-43). 

 Devil's River, Texas. 



Unio bealii Lea. Jour. Acad. Nat. Sci. Phila., V^ol. v, p. 204, PI. xxx, 

 Fig. 273, 1866 ; Observations on the Genus Unio, Vol. ix, p. 26, PI. xxx, Fig. 

 273 (PI. vi, Figs. 44-46). Leon County and Rutersville, Texas. 



The conchologic characters of this form do not widely vary. As may be seen 

 the species only comes from Texas, and contiguous portions of Louisiana. 



The following description may assist in understanding the relation which 

 this form sustains to the common and widely distributed type of the group. 



Shell small, very elliptical, especially in the female, compressed laterally, 

 nninded before, biangulate posteriorly though this character is less marked in 

 the female, which is somewhat regularly rounded, striate; valves rather thin 

 though somewhat thickened anteriorly ; epidermis rather thick, olive-green, in 

 young specimens with occasional rather broad greenish lines along the angles of 

 the posterior umbonal slope; lines of growth numerous, fine and closely arranged, 

 in old specimens often forming raised ridges along the ventral posterior margins ; 

 ligament long, smooth, light horn colored and shining, very narrow; umbones 

 scarcely prominent, close together, rather coarsely undulate, the undulations 

 being concentrically arranged as seen in young specimens; in the young the 



"This is a large male specimen from the W.-ibiish River, Indiana. In it the cardinal 

 teeth are double tii both valves; the posterior cardinal in the left valve is curved dnimtd and is 

 very long and thin, its edges are sharply serrate. 



