AQUATIC MAMMALS 



bases, and the pelage is coarse. Like many of its relatives it is without a 

 tail, differing in this respect from all other aquatic rodents, and it is 

 by no means unlikely that this lack accounts for the fact that (from 

 all accounts) it uses all four feet in swimming. It is partial to beds 

 of reeds but seeks the water when disturbed, swimming and diving with 

 facility. 



Muridae 



Crossomys — one of the Australian water rats, in all three genera of 

 which the fur is dense and soft, and in all the external ears are small 

 but well formed. In this genus the toes are said to be webbed and the 

 tail, which tapers gradually from the body, has a strongly marked swim- 

 ming fringe below. In these water rats swimming is undoubtedly by al- 

 ternate movements of the hind feet, assisted by the tail. 



Hydromys — a second genus of Australian water rat and the only 

 one which I have examined. The feet are partially webbed, and the 

 dorsal outline of the skull straight (as may be the case in the other 

 two). 



Parahydromys — a third genus of Australian water rat, in which the 

 aquatic specialization is said to be somewhat less than in Hydromys. 

 The first and last hind toes are practically unwebbed. 



Dasmyms — a genus of African rodent which is said to be somewhat 

 aquatic, but the only indication of this which is shown by specimens 

 consists of the pelage, which is short, thick and soft. 



Nilopegamys is another genus of aquatic rodent from Africa, known 

 from a single specimen and recently named by Osgood. Its pelage 

 is also soft and dense, the hind feet are slightly enlarged, and the dor- 

 sal outline of the skull has a concavity near the interorbital region. 



Arvicola and Microtus. Several members of the subfamily Micro- 

 tinae (meadow mice or voles) live in bogs or along the banks of 

 streams and swim freely. Perhaps the most aquatic of these is the 

 European water rat (Arvicola), but it has no discernible modifica- 

 tions that are considered really aquatic. 



Ondatra — the muskrat, of the United States and Canada, is the most 

 aquatically specialized of all the Muridae. Its underfur is extremely 

 soft and dense, the hind feet are enlarged and although not com- 

 pletely webbed, the sides of the feet and all the toes are bordered by 

 very heavy fringes of stiff hairs, and the tail is laterally much flattened. 

 Swimming is accomplished by means of alternate thrusts of the hind 

 feet and accompanying horizontal movements of the tail; and I have 



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