UNIO 609 
lateral; beak cavities rather shallow; muscle scars impressed ; 
nacre white, yellowish, salmon or purple, thicker in front. 
Length 96, height 55, diam. 38 mm. 
Length 83, height 53, diam. 37 mm. 
Type locality, Spanish Creek, Charlton County, Georgia. 
Unio polymorphus B. H. Wricut, Naut., XIII, 1899, p. 42.— 
SIMPSON, Syn., 1900, p. 707. 
A large number of specimens of this form from the type 
locality are before me and [| hardly know what to do with 
them. ‘The species, if species it is, seems to stand between 
crassidens and forbesianus in a different way from what i- 
crassatus does. It has the form of forbesianus to some extent, 
but is solider and’has a different epidermis. It resembles 
crassidens in its solidity and the comparatively shallow beak 
cavities. It is very likely a variety of forbesianus. 
UNIO FORBESIANUS Lea. 
Shell subrhomboid, scarcely inflated, inequilateral, subsolid ; 
beaks full and rather high, their sculpture consisting of strong, 
slightly corrugated ridges that run nearly parallel with the 
growth lines; posterior ridge high, angled, often narrowly 
and feebly double below, ending behind in a point or slight 
biangulation at or near the base of the shell; base line straight 
or curved a little; surface rather smooth, but having sub- 
radial plications on the posterior slope; epidermis yellowish 
to olive-green and usually rayed in the young shell, tawny or 
burnt brown and almost or quite rayless in the adult stage, 
nearly smooth, sometimes shining; left valve with two tri- 
angular, rough pseudocardinals and two curved laterals; right 
valve with one pseudocardina!, sometimes with a vestigial one 
above it and one lateral ; beak cavities deeper than in U. crassi- 
dens; muscle scars well impressed: nacre white, biuish, cream, 
salmon or purplish. 
Length &0, height 49, diam. 31 mm. 
Length 74, height 39, diam. 25 mm. 
Tength 63, height 40, diam. 23 mm. 
