THE BEAVER. 



97 



is very small, and all these teeth are rootless, simple, and prismatic, the surface of each tooth being 

 surrounded by a mere border of enamel. The skull is very flat, very wide behind, and furnished with 

 large zygomatic arches ; between the orbits and in front it is much contracted, and there are no 

 post-orbital processes. In the lower jaw the angular portion is twisted so as to form a horizontal ridge. 

 The body is stout and clumsy, the tail very short, and the claws of the fore feet (which are five-toed, 

 as well as the hind ones) are very powerful ; in fact, as Dr. Coues says, " The whole organisation, 

 viewed exteraally, indicates terrestrial and highly fossorial habits." 



The SEWELLEL (Haplodon nifus) is about a foot long, with a tail of an inch or an inch and a half ; 

 its colour is brownish, with an intermixture of black hairs, lighter and more greyish below. The whiskers, 

 claws, and upper surface of the feet are whitish, and the incisor teeth yellow. It inhabits the Washing- 

 ton and Oregon territories, from the Rocky Mountains to the shores of the Pacific, and extends also 

 into the southern portions of Biitish Columbia and the upper parts of California. 



The Sewellel is described as having very much the same habits as the Prairie Dog, living in 

 society, burrowing very readily in the ground, and feeding on roots and berries. Their companies, 

 however, seem to be much smaller than those of the Prairie Dog, and they are said chiefly to frequent 

 spring-heads in rich, moist places. They are described as having the curious habit of neatly cutting 

 off some herb or plant, which, when packed in bundles, they lay out and expose to the sun to dry ; 

 this is probably for the purpose of storing for winter consumption. It seems to be uncertain whether 

 the Sewellel is torpid during the winter, but probably in this respect it varies according to local con- 

 ditions or the coldness of the seasons. Dr. Suchley believes that the Sewellel has several litters of 

 young during the season. The Indians trap them, and esteem them very highly as food. Cloaks or 

 blankets are made of their skins, which are sewn together with fibres derived from the sinews of the 

 Elk and Deer. A robe described by Sir John Richardson was composed of twenty-seven skins. 



FAMILY IV. CASTORID^E. 



Unlike as the Beaver may be to a Squirrel, it yet presents many characters which prove that its 

 nearest affinity is to the animals which compose the group Sciuromorpha. This relationship has indeed 

 been overlooked by many zoologists, but Mr. Alston and 

 Mr. Allen have clearly shown that Professor Gervais was 

 right in placing the Castoridse in close juxtaposition with 

 the Squirrels. The peculiarities which make the apparent 

 discrepancy so striking are indeed chiefly those by which 

 the Beaver is adapted to an aquatic life. 



The Beaver, which is the sole living representative of 

 this family, is a more powerful animal than any of the pre- 

 ceding, and his incisor teeth and the means of working them 

 are especially well developed. The head is large and the 

 skull massive, and furnished with a distinct median 

 (sagittal) crest for the insertion of the strong muscles 

 which move the lower jaw. There are no post-orbital pro- 

 cesses. There are four molars on each side in each jaw, 

 and these are nearly similar in size and structure ; but, 

 contrary to what we have seen in the preceding groups, the first molar is the largest, and the others 

 diminish in size towards the hinder end of the row. The series of teeth in the two sides of the mouth 

 converge toward the front ; and the teeth themselves, which are for a long time rootless, and only 

 close up to form a simple root when the animal grows old, show three folds or loops of enamel on 

 one side, and a single fold on the other: the three folds entering from the outer surface of the tooth 

 in the upper jaw, and from its inner surface in the lower. 



The general form is stout and heavy, especially in the hinder parts; the tail is ,of 

 moderate length, broad, flattened, and covered with a scaly skin ; the feet are all five-toed, the fore 

 pair considerably smaller than the hinder, but all well furnished with claws, and the hinder pair fully 

 webbed to the extremities of the toes. The wrist has a large ossicle, in addition, to those usually 



MOLAR TEETH OF THE BEAVER. 



