UNIO 595 
Type locality, Rio Cosamalcapam, near Chacoltianguiz, 
State of Vera Cruz. Mexico. 
Unio distinctus Cross and Fiscuer, Jl. de Conch., XLI, 1893, 
p. 110;—Fiscner and Crosse, Miss. Scient. Mex., Moll. 
II, 1894, p. 579, pl. Lx1x, figs. 2, 2a. 
Unio semigranosus var. distinctus, VON MARTENS, Biol. Cent. 
Amer., Moll!., 1900, p. 494. 
“Unio distinctus belongs to the group of U. psoricus More- 
let. but it is less elevated, more transverse, more angular in 
front and the beaks are less inflated. It is to some extent inter- 
mediary between that species and U. crocodilarum Morelet, a 
form quite transverse and elongate.” 
UNIo TESTUDINEUS Morelet. 
Shell subequilateral, triangular ellipitical, compressed, solid 
with an olive-green epidermis, with strong concentric growth 
lines, covered densely with tubercles throughout the surface; 
posterior ridge low, scarcely biangulate ; anterior end obliquely 
truncate above; base rounded; beaks rather high, their sculp- 
ture not observed. Left valve with two ragged pseudocard- 
inals and two laterals, right valve with two pseudocardinals, 
the upper compressed and small and one lateral; anterior mus- 
cle scars deep; posterior scars shallow ; nacre coppery-purple. 
Length o1, height 70, diam. 34 mm. 
Rio Usumacinta, Guatemala. 
Unio testudineus Morrier, Test. Nov., os 1849, p. 28.—FIscH- 
ER and Crosser, Miss. Sei Ee srees, fe +571, pls. Lx, fig: 
3; LXx, fig. 3—Srimpson, Syn., 1900, p. 702. 
Unio semigranosus Rerve, Conch. Icon., XVI, 1864, pl. x 
36. 
Unio semigranosus var. testudineus VON Martens, Biol. Cent. 
Amer., Moll., 1900, p. 493. 
This species seems to differ from U. psoricus in being more 
compressed, and in having tubercles all over its surface. 
Unto psortcus Morelet. 
Shell subtriangular, inequilateral, subdepressed, solid, with a 
moderate, sometimes double, posterior ridge; anterior end 
angulated and rounded; beaks rather high but not inflated: 
