CATALOGUE OF MAMMALIA. 



INDIAN MUSEUM. 



Part II. 



Order RODENTIA. 



The Rodentia are Mammals characterized by the following 

 points of structure : — a middle pair of long, curved, rootless, persis- 

 tent incisors ; no canines ; three molars above and below [except 

 Hydromys] ; temporal and orbital fossae of skull confluent, the 

 la'crymal foramen opening within it ; a distinct interparietal present ; 

 scapula narrow, with a deep notch and a well developed acromion ; 

 manus, five or four digits ; pes, three to five digits ; placenta deci- 

 duate and discoidal. 



A general account of the classification and of the genera of the 

 group by E. R. Alston will be found in P. Z. S., 1876, p. 61 ; it is 

 mainly on this paper that the following key of the Indian Genera 

 is based. 



Key of the Indian Genera. 



a. Only one pair of incisors above ; skull with a true alisphenoid 

 canal ; optic foramina rarely confluent; bony palate well de- 

 veloped ; fibula never articulates with the calcaneum ; testes 

 abdominal, descending periodically. [=Simplicidentata.] 



h. Two premolars above and below; post-orbital processes 

 present ; infra-orbital opening very small ; zygomatic arch 

 mainly composed of the malar bone, not supported below 

 by a process of the maxilla ; mandible with the angular 

 portion springing from the lower edge of the bony covering 

 of the lower incisor; fibula separate through life; upper lip 

 cleft; muiHe small, naked; nostrils comma-shaped; tail 

 cylindrical and hairy. [=Sciuridae.] 



c. Incisors compressed. 



d. Limbs united by a flying expansion ; form slender ; tail 

 long. 



B 



