Vol. XII, pp. 127-129 April 30, 1898 



PROCEEDINGS 



OF THE 



BIOLOGICAL SOCIETY OF WASHINGTON 



A NEW GENUS (KEOTOMODON) 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 an) 7 

 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. now , from Nahuatzin, 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; mammpe 

 6; pectoral \ ; inguinal f; general appearance intermediate between. Mi- 

 crotus and Peromyscus of the guati malt nsis group. Skull and teeth unique ; 

 skull broad and rather high ; braincase short and rounded [in X 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 J the basal length of skull. Molars rooted, large, 

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

 enamel loops open throughout; m^ and m 3 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 the loops more nearly 



29— Biol. Soc. Wash., Vol. XII, 1898 (127). 



