SPALACOPODID^E. XV. 33 



1. A. riparius, 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; size 

 medium. (Ped&mys.) 



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

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



*** Teeth as in Ped&mys; fore claws larger than hinder; fur 

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



3. A. p/netorum, LeC. PINE MOUSE. Tail about one- 

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



7. SYHAPTOMYS, Baird. COOPER'S MOUSE. 



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

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



8. FIBER, Cuvier. MUSKRATS. 



1. F. zibeihicus, ( L.) Cuv. MUSKRAT. MUSQUASH. A 

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

 N. Am.; every where. 



FAMILY XV. SPALACOPODID^E. 



(TJie Porcupines.) 



Body more or less armed with spines. Molars rooted, 

 f:f. 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 -family Cercolabince, to which our genus 

 belongs, than to the whole family. 



