XQ 
UNIO. 495 
6. Unio corium. (Tab. XXXI. fige. 4, 4a, b.) 
Unio corium, Sowerby, in Reeve’s Conch. Icon. xvi., Unio, t. 10. fig. 39 (1864) 1; Fisch. & Crosse, 
Miss. Scient. Mex., Moll. ii. p. 5702. | 
Also near U. semigranosus, but more elongated, the summits in 2 of the whole length ; the granulosities near 
the summits arranged in arcuated lines. 
Long. 103 ; alt. vert. 63, alee 59, diam, 384 millim. 
Hab. S.E. Muxico: Chiapas}. 
The type figured by Sowerby has a small distinct sinus at the hinder end of the 
ventral margin; but a specimen in the Berlin Museum from the late Paetel’s collection, 
here figured (figg. 4, 4a, 6), somewhat larger and otherwise agreeing, has scarcely an 
indication of it. 
7. Unio morini. 
Unio morini, Morelet, Test. Noviss. ii. p. 25 (1851)!; Fisch. & Crosse, Miss. Scient. Mex., Moll. 
li. p. 576, t. 60. fig. 2, t. 67. fig. 47. 
Near U. corium, but with the summits still more advanced, in 3-1 of the length; the granulosities smaller and 
more crowded, the fore part inflated, the hinder part more compressed, with two feeble ridges running 
from the summits behind and below; ventral margin straight, a little sinuated behind. 
Hab. N. Guatemata: Rio Usumacinta (Morelet} *). 
In the typical specimen, figured by Fischer and Crosse ”, the inside is bluish-white and 
the two posterior ridges, although feeble, cause a distinct notch at the hinder extremity. 
8. Unio crocodilorum. (Tab. XXXI. figg. 3, 3a, 3, ¢.) 
Unio crocodilorum, Morelet, Test. Noviss. 1. p. 28 (1849); Fisch. & Crosse, Miss. Scient. Mex., 
Moll. ii. p. 577, t. 60. figg. 3-5, t. 67. fig. 3°. 
Unio pliciferus, Sowerby, in Reeve’s Conch, Icon. xvi., Unio, t. 10. fig. 37°. 
Cuneiform, swollen, and minutely tuberculated, rounded before, produced and beaked behind. 
Hab. N. Guatemata: Rio Usumacinta, Province of Peten (Morelet +?); Coban (Mus. 
Berol.). 
Fischer and Crosse 2 distinguish two varieties, 8. semipustu/atus (fig. 4), with tubercles 
in the middle part of the shell only, and y. prestrictus (fig. 5), shorter and more swollen, 
both from the same locality. Inside purple, seldom white in the typical form: white 
in the var. semipustulatus, purple in the var. prestrictus; the colour therefore affords 
no reliable difference. | 
The specimen from Coban belongs to the var. prestrictus. . 
The specimen figured here (figg. 3, 3 a—c), from Paetel’s collection; with the simple 
indication “ Mexico,” looks at first sight rather like U. morini, but on a closer examing- 
tion of the essential characters I find that it agrees better with U. crocodilorum, viz. in 
the declivity of the dorsal margin beginning behind the summits, in the more produced 
