SPALACOPODID^. — XV. 33 



1. A. pennsylvanicus, Ord. Meadow Mouse. Fore claws 

 not longer than hind claws; tail one-third length of 

 head and body, or more. U. S.; generally abundant. 



** Back upper molar with one exterior triangle and a posterior 

 trefoil ; middle upper molar with one internal triangle ; front 

 lower molar with two internal and one external triangle; 

 fore claws not larger than hinder; fur ordinary; aize 

 medium. ( Pedomys.) 



2. A. austerus, LeC. Tail one-third length of head 

 and body, or less. Western States, E. to Michigan. 



*** Teeth as in Pedomys; fore claws larger than hinder; fur 

 dense, silky, mole-like ; size small. (Pitymys.) 



3. A. pinetorum, LeC. Pine Mouse. Tail about one- 

 fourth length of head and body. E. U. S. 



7. SYNAPTOMYS, Baird. Cooper's Mouse. 



1. S. cooperi, Baird. Head short and heavy; fur soft 

 and long. W. States, E. to Ind. 



8. FIBER, Cuvier. Muskrats. 



1. F. zibethicus, ( L.) Cuv. Muskrat. Musquash. A 

 well-known aquatic animal, the largest of our Muridce, 

 N. Am.; every where. 



FAMILY XV. — SPAL ACOPODID^. 



( The Porciipiiies.) 



Body more or less armed with spines. Molars rooted, 

 |^:|-. Toes 4-5 in ours, sub -equal, with long, com- 

 pressed, curved claws; soles warty. Muzzle hairy; 

 upper lip without a groove; chiefly arboreal; nearly all 

 are South American. The above characters apply rather 

 to the sub - familv C ercolahmce^ to which our o-enus 

 belongs, than to the whole family. 



