120 MONOGRAmS OF NORTH AMERICAN RODENTIA. 



Genus OCHETODON, Coues. 



x Mas sp., Aui>. & Bach. 



X Uvtperomyt sp., Wagner. 



= BeUhrodon, LeCo.nte, Proc. Acad. Nat. Sci. Phila. 1S53, 413— Baird, M. N. A. 1857, 447. Not of Watcrh. 



= Ochctodon, Coues, Proc. Acad. Nat. Sci. Phila. 1874, 184. 



Chars. — 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 

 l\[us 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 Reithrodon 

 of Waterhouse. Iu this course, he was followed, in 1857, by Professor Baird, 

 who united two of Audubon and Bach man's species {humilis and lecontei) in 

 one, gave Mus carolinensis, And. & Bach., as a doubtful species of the genus, 

 and described three new ones, R. montanus, R. megahtis, and R. longicauda. 



Although adopting Reithrodon 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 Reithrodon 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 Reithrodon 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 Reithrodon, we are satisfied that the 

 genus w r e 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 ; Culomys being the only one of them that closely approaches ours. 



The following differential diagnosis may doubtless be largely supple- 

 mented with additional characters: — 



