652 SUPPLEMENT. 
Unio guatemalanus (p. 519). 
This species somewhat resembles U. mellews, Lea (Obs. Unionide, vii. p. 68, t. 38. 
fig. 129), from an unknown locality ; but, according to Simpson (loc. cit. p. 597), no 
doubt from ‘“‘ Mexico or Central America.” On comparing my specimens with Lea’s 
description and figure, I find that U. melleus is somewhat less high, more pointed at 
its hinder end, and has distinct waved wrinkles near the summits; whereas in my 
examples of U. guatemalanus the summits are not worn to a larger extent than shown 
in Lea’s figure, and no wrinkles are visible. At all events, the two species appear 
to be nearly allied, and this corroborates Simpson’s observation on the habitat of 
U. melleus. 
Unio manubius (p. 519). 
Simpson (loc. cit.) considers this form to be a variety of the North-American 
U. tetralasmus. 
Unio explicatus (p. 520). 
Simpson (doc. cit. p. 571) regards U. testudineus of Reeve’s ‘ Conchologia Iconica’ 
(nec Morelet) as distinct from U. eaplicatus, Morelet, and names it U. lividus; it is 
said to be also from the Rio Usumacinta. Both U. explicatus and U. lividus are 
placed by him in the genus Lampsilis. 
Metaptera (pp. 481, 520). 
The three species enumerated under this subgenus are placed by Simpson in the 
genus Lampsilis, as well as U. alatus, Say, the type of Metaptera, Rafinesque. 
Unio tamaulipanus (p. 521). 
I cannot find any mention of this species (described by Conrad in 1855) in Simpson’s 
work, 
Unio mitchelli (p. 522). 
Unio mitchell, Simpson, Proc. U.S. Nat. Mus. xix. p. 871, t. 382. figg. 1-3 (1896) °. 
This species is placed by Simpson in the genus Unio, s. str., division Homogene, 
far apart from U. rowelli and U. scamnatus, which belong in his arrangement to 
Nephronaias, division Heterogene ; he thinks that U. mitchelli is allied to U. pigerrimus 
and may be nothing more than a variety of it. 
Unio saladoensis (p. 522). 
A distinct species belonging to the genus Lampsilis, constituting even a peculiar 
group, according to Simpson (oe. cit. p. 569). 
