46 THE CANADIAN NATURALIST. [Feb. 



lofty pines ; in dark, miry wastes, amid fungoid growths, sedge 

 plants, and perpetual decay ; along the banks of tortuous rivers, 

 from their sources — mere mountain burns, trickling down the 

 craggy sides of the Rocky Mountains — to their mingled exit into 

 the Atlantic, as the great St. Lawrence ; — musk-rats live, thrive, 

 and multiply. Cross the snow-clad heights of the Rocky Moun- 

 tains, and descend their western slopes, through hotter lands, to 

 the shores of the Pacific ; from the Rio-Grande to the desolate 

 regions of Arctic America ; through fertile California ; grassy, 

 flower-decked Oregon ; Washington Territory, with its deserts and 

 mountains ; and the densely-timbered wilds of British Columbia, 

 to its junction with Russian America ; on rocky Vancouver Island, 

 as well as on every island of any size in the Gulf of Georgia ; — 

 musk-rats have found their way, built and burrowed. It was 

 once supposed, that the musk-rat had made its way to the Asiatic 

 side of Behring's Straits, but there can be but little doubt the 

 skins obtained from Kamschatka and Tschucktchis are traded, or 

 bartered, from native tribes living on the American shores. 



There are many structural points of similarity betwixt the 

 musk-rats and Arvicolas, or ' field-mice ;' still the peculiarly 

 formed feet, flattened tail, much larger size, and singularities of 

 habit in the former, distinctly separates the two genera. Indeed, 

 the musk-rat seems to fill a gap, as it were, between the field- 

 mice (Arvicolince) and the porcupines (Hystricidce). The sub- 

 family (CasterincB) which the famed beaver represents, connects 

 the squirrels and marmots (Sciurissce), on the one hand, with the 

 gophers (Geomyince) on the other. The teeth of the musk-rat 

 are of arvicoline type. The first and third molars are longer than 

 the second, the second being wider than either of the other two. 

 The grinding surface of the first molar has two indentations or 

 reentrant angles on each side ; the second, two outside and one 

 inside ; the third, three outside and two inside. The first and 

 third grinders have five prisms or projections on their surfaces, 

 the second four. The loops of enamel extending across the tooth, 

 and joining the enamel that encases the surface, completely isolates 

 the patches of dentine ; thus a mill-stone is formed by this most 

 simple contrivance, that improves in grinding power the more it is 

 worked, and never needs roughing with the stone-cutter's hammer. 



In the lower jaw the first molar is much larger than the second 

 and third, which are about equal in length and width. The first 

 having five indentations inside and four outside. The other 



