362 



BULLETIN 56, UNITED STATEB NATIONAL MUSEUM. 



Measurements of IS specimens of Castor ewnadensis frondaior.a 



o All but the last two specimens are in the collection of the American Museum of Natural History. 

 6 Type. 



Family MURID.ZE. 



RATS AND MICE, 



Dentition.- 



C. 



P. 



M. 



= 16. 



^' 1-1 » ^- 0-0' ^ • 0-0' ^"^' 3-3 



Skull with contracted frontals; a short and slender jugal, generally 

 reduced to a splint between the zygomatic processes of the maxilla 

 and squamosal; the lower root of the former process more or less 

 flattened into a perpendicular plate; typically, the infraobital vacuity 

 tall, and wide above and narrow below. Lower incisors compressed; 

 no premolars; molars rooted, or rootless, tuberculate, or with angu- 

 lar enamel-folds. PoUex rudiniental; tail generally nearly naked and 

 scaly. ( Flower and Lydekker.) 



