UNIO 695 
Margaron (Unio) aheneus LEA, Syn., 1852, p. 37; 1870, p. 60. 
The type is a young shell, but I have seen a quantity of shells 
from Lake Ashby, Florida, whose young agree well with it. 
Unio watont B. H. Wright. 
Shell much elongated, compressed, inequilateral, rather thin, 
subrhomboid ; anterior end angled above, somewhat cut away 
below ; base line nearly straight, full just behind the middle ; 
dorsal line straight or slightly curved, being prodticed into a 
low wing; dorsal slope obliquely truncated; posterior ridge 
angled, inclined to be slightly double below; ending behind 
near the base of the shell in a feeble biangulation, the lower 
angle longer; surface concentrically striate; epidermis dark 
brown, showing vestiges of rays, dull or scarcely shining; 
pseudocardinals low, small, not perfectly developed, double in 
both valves; laterals long, straight and delicate; muscle scars 
shallow ; nacre chocolate. 
Length 80, height 30, diam. 15 mm. 
Length 74, height 30, diam. 16 mm. 
Florida. 
Type locality, Lake Woodruff, Valusia Co., Fla. 
Umo waltom Bs H. Wricut, Pr. Ac. N. Sci. Phila., 1888, p. 
114, pl. 1, fig. 3— Simpson, Pr. U. S. Nat. Mus., XV, 1892, 
Po 434, pl. Lex, fo: 7; Syn, 1900, p. 730. 
I have only seen a few specimens of this shell but I have 
always suspected that it was only an elongated, rather delicate 
variety of U. aheneus. ‘The shorter shell, whose measurements 
are given above, seems to hint at a connection, yet from what 
material I have seen I do not feel justified in uniting the two. 
U, waltoni is more sharply and obliquely pointed behind than 
aheneus. ‘The beaks of all the shells I have seen are so badly 
eroded that I can make nothing out of them. 
UNIO ROSTRAFORMIS Lea. 
Shell elongated, subelliptical or subovate, compressed or 
subcompressed, rather thin, inequilateral; beaks scarcely ele- 
vated, compressed, their sculpture consisting of slightly broken 
ridges that run nearly parallel with the growth lines ; posterior 
