106 ZOOLOGY. 



1'incmys, LESSON, Nouv. Tnbl. 11. A., 1842, 12 (typepinetorum). 

 Ucmiotomys, BD., M. N. A., 1857, 515 (type A. riparius, ORD). 

 Pi'domys, BD., op. cit., 517 (type A. austcrus, LEG.). 

 Cliilolus, BD., op. cit., 51C (type A. orcgvmis, BACH.). 



The four sections into which the North American species of this difficult 

 genus fall may be thus distinguished : 



A. Back upper molar with 2 external triangles aud a posterior crescent. 



Middle upper molar with 2 internal triangles. Front lower 

 molar with 3 internal and 2 or 3 external lateral triangles. 

 Ears uiirinmied in front. Soles 6-tuberculate. Fore claws not 

 longer than the hinder ones. Tail about J the length of head 

 and body, or more. Pelage ordinary. Size maximum and 

 medium MYONOMES. 



B. Back upper molar with only 1 external triangle and a posterior trefoil. 



Middle upper molar with 1 internal triangle. Front lower 

 molar with 3 internal and 2 or 3 external triangles (as in 

 Myonomcs). Ear with a rim in Iront of meatus, the anterior 

 and posterior roots of the auricle there meeting. Soles 5-tuber- 

 culate (?). Fore claws not larger than the hinder. Tail about 

 the head and body. Pelage ordinary. Size minimum CHILOTUS. 



(J. Back and middle upper molars as in the last. Front lower molar with 

 only 2 internal and 1 external triangle. Ear unrimmed. Soles 

 5-tubercnlate. Fore claws not larger than the hinder. Tail J 

 the head and body, or rather less. Pelage ordinary. Size 

 medium PEDOMYS. 



U. Molars all as in Pedomys. Ears uurimmed. Soles 5-tuberculate. Fore 

 claws larger than the hinder. Tail about the head and body, 

 or less. Pelage dense, silky, inole-like. Size small PITYMYS. 



Subgenus MYONOMES, Raf. 



Arvicola of most American writers. 



Arvicola, A, Hemiotomys, BAIRD, M. N. A., 1857, 515 (type riparius. Not of Selys-L.). 



Myonomcs, EAF., (type M. pratensis, Eaf., based on "Wilson's Meadow Mouse " = 



A. pennsylvanica, Ord. = A. riparius, Ord). OOUES, Proc. Acad. Nat. Sci. 



Phila,, 1874, 189. 



AKVICOLA (MYONOMES) RIPARIUS, Ord. 



Campagnol or Mcadoio Mouse of Pennsylvania, WARDEN, Descr. U. S., v, 625. 



Meadoic Mouse, WILS., Am. Orn., vi, pi. 50, f. 3. 



Arvicola pennsylvanica, ORD, Guthrie's Geog., 2d Am. ed., ii, 1815, 292 (based on the 



foregoing). HARLAN, Fn. Am., 1825, 144 (in part; quotes Ord, but describes 



pinetorum). 



.1 n-ifitlo i-ijxn-iun, OUD, J. A. N. S. P., iv, 1825, 305 (Philadelphia). 

 Arcicohi riparius loinjipilia, KENN., Agric. Rep. U. S. Patent Oflice, 1850, 304 (West 



Northlield, 111. ; in winter pelage). 



