622 UNIO 
A rather short, solid species with heavy hinge and rude 
sculpture. According to its authors the nacre is tinted with 
rose, while that of mitchelli is white. 
UNIO MITCHELLI Simpson. 
Shell subrhomboid, oblong, moderately convex, rather solid, 
inequilateral, with rather low, somewhat flattened, beaks, 
whose sculpture consists of a few strong, irregular ridges 
running nearly parallel to the growth lines; posterior ridge 
rather low, generally rounded and sometimes double, often 
ending behind in a feeble biangulation; base line straight or 
slightly curved, sometimes a little arcuate; surface covered 
with irregular, rather feeble, concentric ridges and showing 
sometimes on the posterior slope and rarely on the disk a few 
faint corrugations; epidermis olive to black, greenish when 
young, sometimes faintly rayed on the earlier growth; left 
valve with two rather small, but solid, ragged, nearly equal 
sized, pseudocardinals and two remote laterals; right valve 
with one strong pseudocardinal, sometimes with a small second 
one above, and one lateral; beak cavities shallow, showing nu- 
merous scars; anterior scars rather shallow, smooth, posterior 
scars large, round, impressed; nacre white. 
Length 54, height 33, diam. 20 mm. 
Length or, height 58, diam. 33 mm. 
Southern Texas to New Leon, Mexico. 
Type locality, Guadalupe River, Victoria Co., Texas. 
Unio mniitchelli Simpson (in Dall.), Pr. -U. S. Nat. Mus.,. 
XVILE 1806, p. 5; PryU Se Nat isS Cex 1rSeOne ae 
pl. XXX, figs. I-33; Syn, 1000, p.. 7 ET. 
Var. thermg: B. H. Wright. 
Shell with a more decided posterior ridge than the type; 
beak sculpture irregular and broken up, sometimes somewhat 
doubly looped; epidermis smoother and more shining than in 
typical shells. 
Southern Texas. 
Type locality, San Saba River, Menard Co., Texas. 
