263 



CnAPTER XXXIX. 



RODENTS continued — murid^ — beavers — voles — rats — mice. 



Mtjrid^e. The various groups of this family, which seem entitled to rank as sub-famUies, are — 1. The 

 Castorini, or Beavers ; 2. The Arvicolin,«, or Voles ; 3. The DiroDiNi,or Jerboas ; 4. The Spalactni, 

 or Mole Rats ; 5. The Saccomyini, or GoiDhers ; and 6. The Murini, or true Rats and Mice- 



Castorini. 



Aplodontia. Dr. Baird includes the Sewellel (Aplodontia xeporina of Richardson) among the 

 Beavers.* Giebel places it amongst the SpALACiNi.f It is probably intermediate between the Marmot 

 and the Beaver, or the Marmot and the Gopher. Beiag that I sway in doubt, I foUow the line 

 suggested by Baird. 



Its habits are scarcely at all known. It is said to be about the size of, and very like, the 

 Musk-Rat in appearance. Its feet are not webbed ; so we may assume that it is not aquatic. It 

 varies in ct)lour from brown to black. It is confined to a narrow region in "Washington territory, 

 on the north-west coast of North America, extending from the coast to the Rocky Mountains. It is 

 doubtfid whether it wiU be found either on the coast range in the Williamette Valley or on the 

 Cascade Mountains. 



Beavers. — (Map 77.) Naturalists have been much puzzled where to jjlace the Beaver in their 

 systematic arrangements, and it occupies very different places in different systems. Dr. Baird main- 

 tains that it is an aquatic Squirrel, as the Marmots are burrowing Squirrels. It certainly has a 

 good deal in common with the Squirrel, but it seems to me to have still more to do with, the 

 Arvicolin.e ; I consider it a gigantic Vole. The skull, perhaps, is more akin to that of the 

 Squirrel, but there are other characters which show greater affinity with the Mtjrid.e. It has the 

 aquatic habits of many of the Voles, and the scaly tail of the Rat has become a flattened oar in 

 the Beaver as well as the Musk-Rat; in the former with the blade jDlaced horizontally, and 

 working as in the whale, in the latter placed vertically and working as in fishes. 



It was for long a question whether the Old-world and the New-world Beavers were distinct 

 species or not. This has now been settled in the affirmative, chiefly on the strength of anatomical 

 differences. J In outward appearance there is scarcely any apprcciable'difference ; but amongst others 

 the same test, — the difference in the relative proportion of the nasal bones, — which distinguishes 

 the skidl of a lion from that of a tiger, is found also to distinguish these species of Beaver. Pro- 



* Baird, op. cit. p. 353. "British Fossil Mamm. and Birds:" lOG. Owen, 



t Giebel, op. cit. p. 5-27. " Catal. Osteol. Ser. Royal College Surgeons," ii. 1853. No. 



X CuviER, "Ossemeus fossiles," viii. 112. Owen, 21G2. 



