VOL. XII, pp. 127-129 APRIL 30, 1898 



PROCEEDINGS 



OF THE 



BIOLOGICAL SOCIETY OF WASHINGTON 



A NEW GENUS (NEOTOMODON} AND THREE NEW 



SPECIES OF MURINE RODENTS FROM THE 



MOUNTAINS OF SOUTHERN MEXICO. 



BY C. HART MERRIAM. 



Still another genus and one strikingly different from any 

 heretofore described is represented by 57 specimens in Mr. 

 E. W. Nelson's rich collections from southern Mexico. The 

 animals were found living among dense grass at high elevations 

 on Mt. Orizaba, Puebla ; the Cofre de Perote, Vera Cruz ; the 

 mountains at Nahuatzin, Michoacan; and on Mt. Popocatapetl, 

 Mt. Toluca, and others about the valley of Mexico. Those from 

 Mt. Orizaba and the Cofre de Perote are distinct species ; all the 

 others may be classed together as a third species. 



Genus NEOTOMODON nobis. 

 Type, Neotomodon alstoni sp. no v., from Nahuat/in, Michoacan, Mexico. 



Characters. Size of a large Microtus ; ears large and nearly naked ; tail 

 medium or rather short ; fur soft and dense ; plantar tubercles 6; mammae 

 6 ; pectoral { ; inguinal f ; general appearance intermediate between Mi 

 crotus and Peromyscus of the guatemalensis group. Skull and teeth unique ; 

 skull broad and rather high ; braincase short and rounded [in N. alstoni 

 angular and truncate posteriorly in old age] ; zygomata large and broadly 

 spreading, the anterior root deeply notched by anteorbital slit, the outer 

 lamina of which is produced far forward ; incisive foramina very long 

 and open ; diastema the basal length of skull. Molars rooted, large, 

 and very massive, with flat crowns and heavy enamel as in Neotoma; 

 enamel loops open throughout ; m^ and m- 2 essentially alike, each with 

 3 salient enamel loops and 2 deep reentrant angles on outer side and 2 

 salient loops and 1 shallow reentrant angle on inner side, as in Neotoma 

 desertorum, from which the teeth differ in having tfye loops more nearly 



29 BJOL, Soc. WASH., Voi. XII, 1898 (J2?) 



