VOL. XI, PP. 277-279 DECEMBER 17, 1897 



PROCEEDINGS 



OF THE 



BIOLOGICAL SOCIETY OF WASHINGTON 



NELSONIA NEOTOMODON, A NEW GENUS AND SPE 

 CIES OF MURINE RODENT FROM MEXICO. 



BY C. HART MERRIAM. 



The collection of mammals made in Mexico by Mr. E. W. 

 Nelson still contains many novelties. Recently, in looking at 

 the skull of a large White-footed Mouse from the mountains of 

 Zacatecas, supposed to be a. typical Peromyscus, I was startled 

 to find that it had the flat-topped' prismatic teeth of a Wood 

 Rat, Neotoma. Closer examination of the dentition showed that 

 while the 1st and 2d upper and 1st lower molars agree essen 

 tially with those of Neotoma, the 3d upper and 2d and 3d lower 

 differ so materially that it is necessary to erect a new genus for 

 the animal's reception. The skull also is peculiar and unlike 

 either Neotoma or Peromyscus. The most important difference is 

 in the antorbital slit, which does not notch the upper surface of 

 the maxillary root of the zygoma. Another character is the 

 production of the inferior angle of the antorbital slit to form a 

 distinct process. The tail is large and blunt, much as in Neo 

 toma not tapering to a slender point as in Peromyscus. 



The new genus may be defined as follows : 



Nelsonia gen. nov. 



Type. Nelsonia neotomodon sp. nov., from Plateado, Zacatecas, Mexico. 



Diagnosis. Cranial characters: Skull in general resembling that of a 

 large Peromyscus but flatter ; zygomata heavier, less depressed, and more 

 spreading anteriorly ; antorbital slits relatively narrow and only faintly 

 notching upper surface of maxillary root of zygoma ; inferior angle of 

 antorbital slit thickened and protruding forward and outward as a dis 

 tinct process ; audital bullse sub-conical as in Peromyscus and Hodumys, 



62 Bioi,. Sue. WASH., VOL. XI, 1897 (277) 



