SPAIiACOPODID^. — ^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. (Pedomys.) 



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

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



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

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



3. A. pinetorum, LeC. Pike 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. Muskeats. 



1. F. zibethious, ( L.) Cuv. Muskkat. Musquash. A 

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

 N. Am.; every where. 



FAMILY XV.— SPALACOPODID^. 



(The Porcupines.) 



Body more or less armed with spines. Molars rooted, 

 |-: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 Gercolabince, to which our genus 

 belongs, than to the whole family. 



