RODENTIA MURINAE HESPEROMYS, 453 



HESPEROMYS, Waterhouse. 



Hesperomys, WATERHOUSE, Zool. of Beagle, 1839, 75. 

 WAGNER, Suppl. Schreb. Ill, 1843, 510. 

 BCRMEISTER, TMcre 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 Phyttotis, 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 

 Habrothrix 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 1 another sub-genus of equal rank, differing from Wagner and Waterhouse, who 

 give to it full generic rank with Hesperomys, 2ieithrodon, &c. 



1 HOLOCHILUS, Brandt. 



WAGKER, Suppl. Schreb. Ill, 1843, 518. 



Holochilus, BRANDT, Mem. Acad. Imp. Sc. St. Pet. (VI Series,) III, 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 ; inr.er 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 Siymodon are 



