The Tullibee, or "mongrel whitefish" (_Argyrosomus tullibee_), has a deep body, like the shad, with the large mouth of the ciscoes. It is found in the Great Lake region and northward, and very little is known of its habits. A similar species (_Argyrosomus cyprinoides_) is recorded from Siberia—a region which is peculiarly suited for the growth of the _Coregoni_, but in which the species have never received much study. =Brachymystax and Stenodus, the Inconnus.=—Another little-known form, intermediate between the whitefish and the salmon, is _Brachymystax lenock_, a large fish of the mountain streams of Siberia. Only the skins brought home by Pallas a century ago are yet known. According to Pallas, it sometimes reaches a weight of eighty pounds. [Illustration: FIG. 52.—Inconnu, _Stenodus mackenziei_ (Richardson). Nulato, Alaska. ] Still another genus, intermediate between the whitefish and the salmon, is _Stenodus_, distinguished by its elongate body, feeble teeth, and projecting lower jaw. The Inconnu, or Mackenzie River salmon, known on the Yukon as "charr" (_Stenodus mackenziei_), belongs to this genus. It reaches a weight of twenty pounds or more, and in the far north is a food-fish of good quality. It runs in the Yukon as far as White Horse Rapids. Not much is recorded of its habits, and few specimens exist in museums. A species of _Stenodus_ called _Stenodus leucichthys_ inhabits the Volga, Obi, Lena, and other northern rivers; but as yet little is definitely known of the species. =Oncorhynchus, the Quinnat Salmon.=—The genus _Oncorhynchus_ contains the salmon of the Pacific. They are in fact, as well as in name, the king salmon. The genus is closely related to _Salmo_, with which it agrees in general as to the structure of its vomer, and from which it differs in the increased number of anal rays, branchiostegals, pyloric cœca, and gill-rakers. The character most convenient for distinguishing _Oncorhynchus_, young or old, from all the species of _Salmo_, is the number of developed rays in the anal fin. These in _Oncorhynchus_ are thirteen to twenty, in _Salmo_ nine to twelve. The species of _Oncorhynchus_ have long been known as anadromous salmon, confined to the North Pacific. The species were first made known nearly one hundred and fifty years ago by that most exact of early observers, Steller, who, almost simultaneously with Krascheninnikov, another early investigator, described and distinguished them with perfect accuracy under their Russian vernacular names. These Russian names were, in 1792, adopted by Walbaum as specific names in giving to these animals a scientific nomenclature. Five species of _Oncorhynchus_ are well known on both shores of the North Pacific, besides one other in Japan. These have been greatly misunderstood by early observers on account of the extraordinary changes due to differences in surroundings, in sex, and in age, and in conditions connected with the process of reproduction.