UNIO 729 
middle, hardly raised; posterior edge rounded or rather com- 
posed of two nearly rectilinear lines ; anterior margin rounded ; 
hinge margin regularly rounded; cavity of the hinge mem- 
branes (in front of the beaks) narrow, but very obvious ; basal 
margin arquated, a little compressed in the middle, and some- 
times almost contracted in that part; within purple, margin 
livid, posterior submargin iridescent; primary teeth nearly di- 
rect, rather thick, striated; lateral teeth hardly extending be- 
yond the sinus of the hinge margin. 
Var. a. Within white. 
Var. b. Within dull yellowish, 
Length 3.1, height 1.6, diam. over .9 inches.” (Say, emend- 
ed). 
Type locality, a stream a few leagues from Vera Cruz, Mex- 
ico. 
Unio purpuriatus SAy, New Harm. Diss., 1831.—Conrap, Pr. 
Ae Nat. Sat Phila, VI; 1853, p.. 255- 
? Unio medellinus FiscHerR and Crossr, Miss. Sci. Mex., 
Moll. II, 1894, p. 603.—von Martens, Biol. Cent. Am., 
Moll., 1900, p. 517.—SIMPSON, Syn., 1900, p. 592. 
Unio (Lampsilis?) purpuriatus Frierson, Naut., XXV1, 1912, 
p. 22; pl. 111; figs. 4, 5. 
“It resembles U. purpureus, nob., but differs in having the 
teeth more direct; in the lateral teeth being shorter, with re- 
spect to the sinus of the hinge margin; in having the greatest 
width at the middle of the posterior margin, etc. In the young 
and middle-aged specimens the radii are very distinct, but are 
obsolete in old specimens. ‘The umbones are widely decorti- 
cated in age, but seldom are they so deeply eroded as to dis- 
close the waxen-colored stratum. It may be considered as 
the Mexicon analogue of the purpureus.” (Say). 
This species has never been satisfactorily identified. Say 
did not figure it and his types seem to have disappeared. Con- 
rad was the first to identify it with the medellinus of Lea. In 
this he has been followed more or less dubiously by later writ- 
ers and by myself in the Synopsis. Von Martens (1. c., p. 503), 
states that there are in the Berlin Museum two specimens from 
