522 MOLLUSCA. 
Unio mitchelli. 
Unio mitchelli, Simpson, Dall, Proc. U. 8S. Nat. Mus. xviii. p. 5 (1895) *. 
Hab. N.W. Mexico: Rio Salado, near Nuevo Leon (Dr. Mearns'). Also in Texas }. 
“Probably groups with U. rowelli and U. scamnatus.” 
Unio saladoensis. 
Unio saladoensis, Lea, Proc. Acad. Phil. 1860, p. 8305’; Journ. Acad. Phil. (2) iv. p. 370, t. 65. 
fig. 195°; Obs. Gen. Unio, viii. p. 50, t. 15. fig. 195°. 
Rounded on both sides, yellowish-green, with many darker rays ; cardinal teeth lamellar. 
Long. 80; alt. vert. 18, ale 22, diam. 13 millim. Vertices in 3 long. 
Hab. N.E. Mexico: Rio Salado, State of Nuevo Leon (Berlandier 1~*). 
Has much the aspect of a young shell. 
Unio petrinus. 
Unio petrinus, A. Gould, Proc. Bost. Soc. Nat. Hist. v. p. 228 (1855) *; Lea, Obs. Gen. Unio, viii. 
pp. 41, 54, 104°; Synops. Fam. Unionide, ed. 4, p. 100 (1870) *. 
Hab. * Mexico. 
The only Unio of ‘subrotundate form” enumerated by Lea? among the species 
from Mexico and Central America, with the indication “ Llanos riv., Mex.”; but 
A. Gould ! says expressly “ Llanos river, Texas.” 
Unio scamnatus. 
Unio scamnatus, Morelet, Test. Noviss. i. p. 30'; Lea, Obs. Gen. Unio, vii. p. 77°. 
See antea, p. 507. 
Unio rugoso-sulcatus. 
Unio rugososulcatus, Lea, Proc. Acad. Phil. 1866, p. 33°; Journ. Acad. Phil. (2) vi. p. 266, t. 34. 
fig. 81°; Obs. Gen. Unio, xii. p. 26, t. 34. fig. 81 °. 
Locality unknown. Lea supposes it to be from Central America and compares the 
species with his U. newcombianus, but it is much longer. As regards its resemblance 
to U. rubicundus, see anted, p. 514. 
Unio metallicus. 
Unio metallicus, Say, New Harmony Disseminator of Useful Knowledge, 1831, p. 6'; Lea, 
Synops. Fam. Unionide, ed. 4, p. 61 (1870) *; Fisch. & Crosse, Miss. Scient. Mex., Moll. ii. 
pp. 615, 616°. 
Hab. Mexico, perhaps from the Lake of Chalco (Maclave 18), 
Lea? and Fischer and Crosse * refer this species to U. cuprinus, Lea, but, to judge 
from Say’s description, I am not at all satisfied with this identification. Perhaps it 
