58 REPORT OF NEW JERSEY STATE MUSEUM. 



Odocoileus americana Rhoads, Mam. of Pa. and N. J., 1903, 



p. 24. 



D orcelaphus vir ginianus Rhoads, Proc. Acad. Nat. Sci. Phila., 

 1897, P- 25. 



Order QLIRES. 



Gnawing Mammals. 



Here belong our rats, mice, squirrels, rabbits, etc., all of 

 which agree in a remarkable arrangement of the teeth, which at 

 once separates them from all other mammals. The incisors 

 or front teeth, two in each jaw, are curved and grow continu- 

 ously from, the base, as their edges wear away from rubbing 

 against each other during the process of gnawing, which is car- 

 ried on in precisely the same way whether it be the house mouse 

 making inroads into our cheese, or the beaver cutting down forest 

 trees for his dam. 



There are no canine teeth at all in the rodent's jaws and a 

 broad gap extends from the incisors to the flat topped grinders, 

 or molars, set close together, four on each side in the back of 

 the mouth. Rodents are for the most part small animals with 

 short legs and sharp claws on the toes. They are represented by 

 numerous species, widely distributed and adapted for all kinds 

 of life, terrestrial, fossorial, arboreal, serial and aquatic. The 

 several families to which our New Jersey species belong, may be 

 distinguished as follows : 



a. A pair of small rudimentary incisor teeth situated behind the large ones 

 in the upper jaw. leporidae (Rabbits.) 



aa. No rudimentary incisors. 



b. Hair thickly interspersed with sharp spine like quills. 



ERETHizcNTiD^ (Porcupines.) 

 bb. No spines present. 



c. Lower leg bones (tibia and fibula) fused together at the lower 

 ends ; Mouse Tribe. 

 d. Hind legs long, tail longer than head and body. 



ZAPODiD^ (Jumping Mice.) 

 dd. Hind legs short, tail not exceeding the head and body. 



MURiD^ (Mice and Rats.) 

 cc. Lower leg bones free. Squirrel Tribe. 



e. Tail broad and flat, naked. castorid^' (Beavers.) 



ee. Tail normal, bushy. sciurid^ (Squirrels.) 



