UNIO Fy 
to be this species and it seems to be a true Unio, the marsupium 
occupying nearly the entire length of the outer gills as a smooth 
pad. I have not been able to examine the beak sculpture of this 
species. 
I am quite sure that Philippi’s Umo nuculinus which has 
been figured for the first time by von Martens in the Biologia 
is a delicate young female aratuts. 
UNIO GRANADENSIS Lea. 
Shell rather small, rhombovate, subintlated, somewhat solid, 
with a well-developed posterior ridge; surface slightly and ir- 
regularly concentrically sulcate, covered with a dark brown or 
blackish epidermis, which sometimes appears slightly silky 
when fresh; dorsal line strongly curved; basal line less curved 
or nearly straight ending in a rounded point behind at a level 
with or just above the base line; anterior end sometimes a 
little angulate but rounded; left vaive with two ragged, sub- 
compressed pseudocardinals and two short, curved laterals; 
right valve with one pseudocardinal, sometimes with a vestigial 
one above, and one lateral, sometimes with a feeble second one 
below it; beak cavities moderate; muscle scars impressed ; 
nacre whitish or yellowish, soiled. 
Length 37, height 24, diam. 18 mm. 
Lake Nicaragua. 
Umio granadensis Lra, Pr. Ac. N. Sci. Phila., XII, 1868, p. 95; 
Jl. Ac. N. Sci. Phila., VI, 1868, p. 203, pl. x11, fig. 103; Obs., 
XII, 1869, p. 53, pl. xLu, fig. 103.—Simpson, Syn., 1900, p. 
744- 
Margaron (Unio) granadensis Lea, Syn., 1870, p. 35. 
The male and female shells do not appear to differ greatly, 
the latter is probably a little fuller at the base. This species 
is larger, solider and more inflated than U. aratus and may be 
always distinguished from it by having a nearly black epider- 
mis, while that of aratus is much lighter colored. Yet the re- 
semblance is sometimes rather close and Dr. Lea placed several 
young granadensis in the tray containing his aratus. I am 
inclined to believe that von Martens has figured one or two 
specimens of this species for aratus. 
