504 | MOLLUSCA. 
Var. chapalanus, nn. (Tab. XXXVI. figg. 5, 5a.) 
Somewhat higher comparatively, especially in its hinder part; brownish-yellow, with some green rays; 
ventral margin scarcely concave ; cardinal teeth more feeble ; inside white. 
Long. 60; alt. vert. 314, alee 32, diam. 20 millim. Vertices in j long. 
Hab. Centrat Mexico: Laguna de Chapala, a large lake situated on the elevated 
plain of Central Mexico, discharging its waters by the Rio Grande de Santiago 
into the Pacific (Deppe and Schiede, in Mus. Berol.). 
From U. poeyanus, which belongs also to the Pacific slope of Mexico, this form is 
distinct by the comparatively higher shell, the height being in chapalanus a little 
more than half, in poeyanus a little less than two-fifths the length. 
26. Unio popei. 
Unio popeii, Lea, Proc. Acad. Phil. 1857, p. 102°; Journ. Acad. Phil. (2) iv. p. 372, t. 66. 
fig. 197°; Obs. Gen. Unio, viii. p. 54, t. 66. fig. 197°; Sowerby, in Reeve’s Conch. Icon. 
xvi., Unio, t. 81. fig. 480*; Stearns, Proc. U.S. Nat. Mus. xiv. p. 104 (1891) ’; Fisch. & 
Crosse, Miss. Scient. Mex., Moll. ii. p. 605 °. . 
Lower and more compressed than the preceding (U. aztecorum), the fore part more produced, the hinder part 
comparatively more elevated. 
Hab. N.E. Mexico: Rio Salado, Nuevo Leon (Capt. Pope !*). 
Also occurs in Texas. 
27. Unio poeyanus. 
Unio poeyanus, Lea, Proc, Acad. Phil. 1857, p. 85°; Journ. Acad. Phil. (2) iii. p. 815, t. 82. 
fig. 80°; Obs. Gen. Unio, vi. p. 35, t. 32. fig. 30°; Sowerby, in Reeve’s Conch. Icon. xvi., 
Unio, t. 90. fig. 486°; Fisch. & Crosse, Miss. Scient. Mex., Moll. ii. p. 606 °. 
Somewhat smaller than U. pope, and lower, especially in the hinder half; the ventral margin more 
sinuated ; periostracum finely granulated. 
Hab. 8.W. Muxico: Rio de las Balsas, near Coyucan, Guerrero (Poey !~). 
28. Unio microdon, (Tab. XXXV. figg. 1, 1 a-c.) 
Unio microdon, v. Mart. Sitzungsb. Ges. nat. Freunde, Berlin, 1887, p. 107 '. 
Testa elliptica, modice convexa, valde inzequilatera, solida, concentrice leviter striatula, intus albida; antice 
rotundata, margine ventrali magis ascendente, postice obtuse declivi rostrata; margo ventralis medio et 
postice subrectus ; vertices subplani, detriti; dentes cardinales perparvi, tuberculiformes, in valva dextra 
unus subtetragonus, levis, apice leviter crenatus, in valva sinistra duo, anterior subtrigonus, levis, posterior 
compressus, acie distincte crenulata; dentes laterales elongati, leviter arcuati. 
a. Long. 107; alt. vert. 57, ale 48, diam. 34 millim. Vertices in 
b. 45 93 ; ” 50, » % 4, 29 ” ” 
Hab. N. Guatemaa: Rio de las Salinas (Stol/'). 
long. 
Ole co [bo 
29 
