120 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
Genus OCHETODON, Coues. 
x Mus sp., AuD. & BACH. 
>< Hesperomys sp., WAGNER. 
— Reithrodon, LECONTE, Proc. Acad. Nat. Sci. Phila. 1853, 413.—Barrp, M. N. A. 1857, 447. Notof Waterh. 
= Ochetodon, Cours, Proc. Acad. Nat. Sci. Phila. 1874, 184. 
Cuars—With the general appearance of Mus proper, but the essential 
characters of Hesperomys, except that the superior incisors are deeply grooved 
lengthwise. Tail about as long as the head and body. 
The occurrence in North America of sigmodont mice with sulcate inci- 
sors was first made known in 1841 by Audubon and Bachman, who described 
Mus humilis. Their animal was almost immediately referred to Hesperomys 
by Wagner. These authors overlooked, or, at any rate, did not take into 
special consideration, the remarkable condition of the upper incisors, and it 
was not until twelve years subsequently, in 1853, that Major LeConte took 
up this point and referred a species to the South American genus Retthrodon 
of Waterhouse. In this course, he was followed, in 1857, by Professor Baird, 
who united two of Audubon and Bachman’s species (humilis and lecontez) in 
one, gave Mus carolinensis, Aud. & Bach., as a doubtful species of the genus, 
and described three new ones, R. montanus, R. megalotis, and R. longicauda. 
Although adopting Retthrodon after Waterhouse, Professor Baird com- 
ments at length upon the obvious differences between the North American 
mice with grooved incisors, and the several species of Retthrodon from South 
America, expressing his surprise at the re-appearance of the genus in the 
United States. Without an opportunity of direct comparison, however, he 
refrained from separating the North American Ochetodon from Reithrodon, 
although he indicated some of the prominent distinctions. 
We regret that, like Professor Baird, we are unable to make the direct 
comparisons of @ezthrodon and Ochetodon that are needed, having neither skins 
nor skulls of the former for” examination. Judging from the figures and 
descriptions that have been published of Rezthrodon, we are satisfied that the 
genus we have founded will prove valid; and, indeed, we should not be sur- 
prised if the grooved incisors proved to be the chief character that Ochetodon 
and Reithrodon share in common. As is well known, the South American Sig- 
modonts are almost without exception widely different from the North Ameri- 
can ; Calomys being the only one of them that closely approaches ours. 
The following differential diagnosis may doubtless be largely supple- 
mented with additional characters :— 
