104 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
apology in this instance if medanophrys turns out to be simply meaicanus. 
At first, we referred our specimens to the latter with little hesitation; but, on 
reviewing the subject, they show so many differences from M. De Saussure’s 
description that we cannot effect an identification. In general dimensions, 
the two species, if such they are, seem nearly the same; but in mezicanus, 
the tail is only longer than the body alone, never even equaling the head and 
body together; while in all our specimens the tail is considerably longer than 
the head and body. This, however, taken alone, we should not consider a 
specific difference, after our experience with Hesperomys “‘myoides” and 
“boylii”; but there are other differences. De Saussure speaks of grayish- 
white under parts, with yellowish on the chin and breast; but in these speci- 
mens the whole under parts are as uniformly pure white as in dewcopus. He 
says the hind feet are brown; in our animal, they are pure white, with a defi- 
nite dusky area at the base of the metatarsus The tail in his animal is 
described as white below; in ours, the bicoloration is not so evident as this 
would imply. Finally, he makes no mention of the singularly conspicuous 
black ring around the eye. All things considered, it is most probable that De 
Saussure had in view an entirely different animal. 
The skull, as already stated, is extremely similar to that of Hesperomys 
leucopus, the species thus falling legitimately in the restricted group, of which 
leucopus is typical. The chief difference is the presence of a distinct bead on 
the margin of the orbits, traceable nearly to the occiput. This, however, we 
cannot consider as even subgeneric; for, as elsewhere stated, it is only the 
smallest and most delicate Hesperomys that are entirely devoid of this crest, 
which makes its appearance with a very slight increase in the general size 
and vigor of any species. The dentition shows nothing peculiar. The pal- 
ate, as in H. leucopus, ends as a simple transverse shelf opposite the last 
molar—a feature by which, as well as by its general slenderness, elongation 
of rostrum, &c., it is distinguished from that of Oryzomys; the latter agree- 
ing in the development of a slight orbital bead. Skull No. 3+ measures 
1.20 in length by 0.64 in breadth, thus obviously exceeding that of deucopus. 
The coronoid process appears extremely short and slight, merely a little spicu- 
lum; the bullze osseze are noticeably small. 
Two female specimens show two pairs of inguinal mammee and one axil- 
lary pair. A note of Professor Sumichrast’s, accompanying one of these, 
gives the following particulars :—‘ Nov. 30, 1862. Found among the leaves 
