RODENTIA—MURINAE—HESPEROMYS, 453 
HESPEROMYS, Waterhouse. 
Hesperomys, Waternouse, Zool. of Beagle, 1839, 75. 
Waener, Suppl. Schreb. II, 1843, 510. 
Burmeister, Thiere Brasiliens, I, 1854, 162. 
Form, generally murine ; tail variable, scant haired. Molars diminishing from first to last ; elongated, the sides indented, 
the crowns with a single longitudinal furrow. Young; teeth with a double longitudinal series of tubercles ; when worn, 
the molars, with angular indentations of the enamel, more or less elongating. 
The typical North American species of this genus have the general appearance of Mus, with 
their long tails, large ears, and quick movements. They have, however, a more hairy tail, and 
the anterior molar teeth have only two tubercles in the transverse series, or two series of tubercles 
longitudinally inserted, instead of three, as in the genus Mus. 
Most of the species have white feet, and the tail whitish, with a darker stripe above. They 
vary in the size and hairiness of the ears, the length of the feet and tail, and in the color. 
There is not much variation in the skull. 
The genus Hesperomys, as above constituted at the head of this article, is of very great extent, 
embracing a large proportion of the American Muridae. It is, properly, the type of the division 
of Sigmodontes, the general remarks respecting the latter applying more particularly here than 
to the other genera. 
Within the limits as assigned above to Hesperomys there are considerable variations of greater 
or less importance which induced Waterhouse, the chief authority in respect to the American 
Murines, to establish several sub-genera for the South American species, based upon the varia- 
tion in the folding and pattern of the enamel, the comparative length of the snout, tail, feet, 
and fur, and the existence of claws or nails on the thumb of the hand. Finding, however, 
that the characters derived from this feature cannot be relied on in all cases, even for specific 
differences, and that the others mentioned seemed more or less intangible, our author, after 
erecting the genera Scapteromys, Oxymicterus, Habrothrix, Calomys, and Phyllotis, subsequently 
combined them all into one genus, Hesperomys, which has been adopted by most writers. There 
are, however, sufficient grounds for arranging the South American species of this genus with sub- 
genera, corresponding in the main with those originally given by Waterhouse, excepting that, 
as suggested by Wagner, Oxymicterus and Scapteromys may be conveniently combined, as also 
Habrothriz and Phyllotis. This would leave three sub-genera, for which, with Burmeister, the 
names Calomys, Habrothrix, and Oxymicterus, may be retained. Burmeister, however, makes 
Holochilus' another sub-genus of equal rank, differing from Wagner and Waterhouse, who 
give to it full generic rank with Hesperomys, Reithrodon, &c. 
1 Hotocurtus, Brandt. 
Wacner, Suppl. Schreb. III, 1843, 518. 
Holochilus, Branpt, Mem, Acad. Imp. Sc. St. Pet. (VI Series,) II, 1835, 428. 
Burmeister, Thiere Bras. I, 1854, 162. 
General appearance rat-like. Upper lip not completely split, hairy above. Tail long. Molars short, broad; last upper 
molar as long as the first ; inner side of the central lower molar with two indentations. 
In size the species of this genus equal the large rats, the body of one measuring nine inches. The upper lip, instead of 
being fissured to the nose, has its upper portion hairy, with the exception of a little fold of skin below. The molars are 
very large, the third upper as long or longer than the second, and equal to the first. The genus differs from Hesperomys, 
which has the teeth becoming smaller from before behind, in lacking this progression. The relationships to Sigmodon are 
