The American grayling (_Thymallus signifer_) is widely distributed in British America and Alaska. In the Yukon it is very abundant, rising readily to the fly. In several streams in northern Michigan, Au Sable River, and Jordan River in the southern peninsula, and Otter Creek near Keweenaw in the northern peninsula, occurs a dwarfish variety or species with shorter and lower dorsal fins, known to anglers as the Michigan grayling (_Thymallus tricolor_). This form has a longer head, rather smaller scales, and the dorsal fin rather lower than in the northern form (_signifer_); but the constancy of these characters in specimens from intermediate localities is yet to be proved. Another very similar form, called _Thymallus montanus_, occurs in the Gallatin, Madison, and other rivers of Western Montana tributary to the Missouri. It is locally still abundant and one of the finest of game-fishes. It is probable that the grayling once had a wider range to the southward than now, and that so far as the waters of the United States are concerned it is tending toward extinction. This tendency is, of course, being accelerated in Michigan by lumbermen and anglers. The colonies of grayling in Michigan and Montana are probably remains of a post-glacial fauna. [Illustration: FIG. 81.—Michigan Grayling, _Thymallus tricolor_ Cope. Au Sable River, Mich. ] =The Argentinidæ.=—The family of _Argentinidæ_, or smelt, is very closely related to the _Salmonidæ_, representing a dwarf series of similar type. The chief essential difference lies in the form of the stomach, which is a blind sac, the two openings near together, and about the second or pyloric opening there are few if any pyloric cæca. In all the _Salmonidæ_ the stomach has the form of a siphon, and about the pylorus there are very many pyloric cæca. The smelt have the adipose fin and the general structure of the salmon. All the species are small in size, and most of them are strictly marine, though some of them ascend the rivers to spawn, just as salmon do, but not going very far. A few kinds become landlocked in ponds. Most of the species are confined to the north temperate zone, and a few sink into the deep seas. All that are sufficiently abundant furnish excellent food, the flesh being extremely delicate and often charged with a fragrant oil easy of digestion. [Illustration: FIG. 82.—Smelt, _Osmerus mordux_ (Mitchill). Wood's Hole, Mass. ]