210 



MONOGRAPHS OF NORTH AMERICAN RODENTIA. 



of a sixth is often seen. The seel ion may readily be differentiated from ils 

 North American congeners by exclusion, thus : — It lacks the peculiar crescent 

 of the last molar of Mtjonomes ; it wants the peculiar auricular characters of 

 Chilotus; and it has nor the enlarged fore claws and glossy pelage of Pitymys. 

 The section was based upon the Arvicola austerus of LeConte by Baird, 

 who added to it two other species, A. haydeni and A. cinnamomeus, neither of 

 which, however, is distinct. Haydeni leads into a remarkable form from the 

 plains, very different, in its extreme development, from austerus, anil still more 

 unlike any other North American species. The discussion of this form is 

 presented in a subsequent article. We insert here the measurements of our 

 skulls of Pedomys, and then proceed to consider P. austerus. 



Table LIU. — Measurements of nineteen skulls 0/ Pedomys austerus. 



* 13159-60-61-68 : animals not full grown ; measurements oxcluded ffcom the averaging, 

 t Type of cinnamomeus. I Type °f luiydeni. 



ARVICOLA (PEDOMYS) AUSTERUS, LeC. 

 Prairie Meadow Mouse. 



Arvicola austerus, LeConte, Proc. Acad. Nat. Sci. Phila. vi, 1--:.:'., 405 (Racine, Wis. ; type, No. 2240, Mns. 

 Smiths.). — Aud. & Bach., Q. X. A. iii, 1854, 289 (based on LeConte's description). — Kenni- 

 COTT, Agric. Rep. U. S. Patent Office for 18r>G (1857), 97, pi. xii, upper fig. (Illinois). 



