﻿TRTTOGONIA 



321 



the species is quite variable, I place it here as a variety. Occa- 

 sional specimens found as far north as southern Ohio seem to 

 stand somewhat between the two forms. 



Tritogonia nobilis (Conrad). 



Shell solid, inflated, inequilateral ; beaks full and hig-h, 

 turned forward over a strong lunule that passes underneath 

 them, their sculpture consisting apparently of doubly-looped, 

 zigzag- bars; anterior end rounded, sometimes slopingly trun- 

 cate or angled above; base incurved in front of the pos- 

 terior ridge; posterior ridge double, with a radial depression 

 in front of it, and sometimes one above it ; surface generally 

 having strong, irregular growth lines and more or less covered 

 with tubercles. There is usually a row of rounded tubercles 

 running down the front angle of the posterior ridge and an 

 irregular, sometimes double, radial row of elongated knobs in 

 front of the middle of the shell and these are stronger than the 

 pustules on the rest of the shell ; dorsal slope having curved 

 nodulous or subnodulous ridges; epidermis brown; pseudo- 

 cardinals double, strong and ragged in the left valve, single 

 in the right, often a good deal split up; laterals straight, dbu- 

 ble in the left valve, single or occasionally semi-double in the 

 right; beak cavities rather deep; dorsal scars in a row under 

 the beaks : anterior scars impressed, rough ; posterior scars 

 shallow : nacre white or dull purple, iridescent behind. Male 

 shell subquadrate ; female shell drawn out behind at the biang- 

 ulate termination of the posterior ridge so that it is often 

 wedge-shaped when viewed from above, less inflated in pro- 

 portion to length than the male shell. 



Length (male) 80. height 6q, diam. 47 mm. 



IvCngth (female) no. height 76. diam. 47 mm. 



Length (female) 114, height yy, diam. 50 mm. 



Red River of the North to Mississippi ; Louisiana ( the type 

 coming from Bayou Teche) ; west into eastern Texas. 

 Unio nobilis Co.vrad. (part), Jl- Acad. N. Sci. Phila.. IT. 1854, 



p. 297. pi. XXVTT, fig. 3. 



Quadrula asper, (part), Simt'Son, Syn., 1000, p. 776. 



