170 Merriam Descriptions of Nine N&w Mamma Is. 



the transverse loops long and narrow, the inner reentrant angles 

 about twice as deep as the outer ; first lower molar with anterior 

 loop double, forming a projecting antero-external loop and an 

 internal lateral loop. 



Mr. Nelson says of it : "A small wood rat was found living in 

 crevices in the rocks, at an elevation of 12,000 feet, on the north 

 slope of the Sierra Nevada de Colima." This is in the upper 

 fir belt. 



At Zapotlan, in the valley below, he obtained five specimens 

 of a form similar to the present but slightly larger and with con- 

 color tails. 



Genus Sitomys. 



Among the small rodents collected are numerous specimens 

 of two mice which in general appearance look almost precisely 

 like the common house mouse (Hits musculus), but are still 

 smaller and have shorter tails. They may be roughly separated 

 into two series, according to size. The smaller is a form (or 

 subspecies) of Sitomys taylori, which was described by Mr. Old- 

 field Thomas a few years ago from specimens obtained at San 

 Diego, Duval county, Texas; the larger apparently is an unde- 

 scribed species, here designated as 



Sitomys musculus sp. nov. 



Type No. Hill tf ad. U. S. National Museum (Department of Agri- 

 culture collection). From near Colima City, Mexico, March 0, 1892. 

 Collected by E. W. Nelson. (Original number, 2055. ) 



(in millimeters, taken in flesh by collector). 

 Total length, 128; tail vertebra^, 48 ; hairs, 1 ; hind foot, 1.7 ; ear 

 (in dry skin) from anterior root, ").">. 



General Characters. In size, color, and external appearance 

 Sifnmys musctiln* looks almost exactly like a small common 

 house mouse (Max >/<//.^-/'///s), except that the tail is shorter. It 

 is smaller than any known species of MOW//X except - s '. M///O/V, 

 from which it differs in being somewhat larger, with longer ears 

 and tail and larger hind feet. It is not quite so dark as typical 

 S. taylori, either above or below. The hind feet measure 16 or 17 

 mm., while those of S. taylori measure only 13 or 13.5. Twenty- 



