UNIO 79 
like declivis with the base line almost straight and forms with 
something of its shape but nearly smooth. 
Frierson, (1. c.), considers declivis to be specifically distinct 
from tetralasmus with geometricus Lea as a synonym. 
Var. sayt Ward. 
Shell rhomboid, with the dorsal and ventral lines very slight- 
ly curved; dorsal slope decidedly obliquely truncated; beaks 
rather full and high, their sculpture strong and distinct; pos- 
terior ridge well developed, rounded and ending near the base 
of the shell in a decided point; surface yellowish or greenish- 
ash, generally with darker, concentric bands ; epidermis some- 
times smooth, more commonly delicately, concentrically wrink- 
led; nacre bluish-white. 
Length 82, height 40, diam. 25 mm. 
Ohio River system. 
Type locality, Walnut Creek and Ohio Canal, Circleville, O. 
Unio sayi Warp (in Tappan), Am. Jl. Sci, XXXV, 1839, p. 
268, pl. 11, fig. 1.—Conrap, Monog., XI, 1838?, p. 102, pl. 
iv, as. 2.—— Kuster, Conch... Cab. Unio, 1861, \ps.246, pl: 
EK, Le. FT; 
Unio savanus B. H. Wricut, Check List, 1888. 
Unio electrinus Reeve, Conch. Icon., XVI, 1865, pl. xxv, fig. 
121. 
Unio tetralasmus var. sayi SIMPSON, Syn., 1900, p. 74T. 
Sometimes becomes quite dark and elongated and I have 
a series of intermediates before me, which shows a gradual 
transition to typical U. tetralasmus. 
The entire distribution of the species and all its varieties 
is as follows: 
Lower Mississippi drainage north to about latitude 40° ; 
Ohio River system; Alabama River system and southwest 
through Texas into northern Mexico. Not reported, so far 
as I know, from the Tennessee and Cumberland rivers. 
UNIO COLUMBENSIS Lea. 
Shell rather elongated, rhomboid, inequilateral, somewhat 
solid, convex or subinflated; beaks only moderately full and 
elevated, their sculpture not observed; posterior ridge full, 
