UNIO 623 
Unio thermgi B. H. Wricut, Naut. XII, 1898; p. 93.—Srmp- 
SON, Pr ng och . ila 1900, p. 79, pl. Iv, fig. 5; Syn., 
LQOO; Pp. .7 12. 
Var. elongatus n. v. 
Shell considerably elongated, biangulate and slightly com- 
pressed behind; epidermis rather smooth, greenish-brown ; 
beak sculpture irregularly doubly looped. 
Length 80, height 43, diam. 24 mm. 
Guadalupe River, Kerr County, Texas. 
Much longer in proportion to its height than the type or the 
variety iieringi!, but having -the same kind of epidermis and 
beak sculpture as the latter. 
In deference to the opinions of some of our best concholo- 
gists | have reduced the form called theringi to the rank of a 
variety of mitchell:. Typically the two are quite distinct but 
there seem to be many intermediate forms. Unio mitchelli is 
apparently close to U. pigerrimus, but from the figures and 
description of the latter, it is a shorter, much solider form, 
with stronger teeth, and hinge plate, and much more rudely 
sculptured surface. 
UNIO SPHENORHYNCHUS Fischer and Crosse. 
Shell very inequilateral, elongated, arcuate, subinflated, its 
greatest diameter being opposite the beaks, from which to a 
point one-third of the way from the posterior end there is a 
gradual narrowing and from this point to the posterior end 
there is a rapid slope, solid; posterior ridge rather well devel- 
oped. scarcely double; surface strongly concentrically striate, 
and having a few, short, subobsolete, radial plications ; epider- 
mis brownish-black ; beaks moderately full, their sculpture not 
observed: left valve with two strong pseudocardinals and two 
remote curved laterals; right valve with one strong, lacerated 
pseudocardinal and a faint tooth above; anterior scars deep 
and rough; posterior scars shallow; nacre yellowish in the 
