362 



BULLETIlSr 5(3, UKITED STATES NATIOI^AL MUSEUM. 



Measurements of 13 specimens of Castor canadensis frondator.n 



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

 6 Type. 



Family I^IURID^. 



RATS AND MICE. 



Dentition. — I. 



C. 



0-0 . p 0-0 . 

 0-0' -^" 0-0' 



M. 



= 16. 



1- 



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 ; tj^pically, the inf raobital vacuity 

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

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

 lar enamel-folds. Pollex rudimental; tail generally nearly naked and 

 scaly. ( Flower and Lydel^Tcer.) 



