Jordan and Evermann. Fishes of North America. 491 



Yellowstone Lake; it is quite evident that trout do pass over in this way; and it is almost cer- 

 tain that Yellowstone Lake was stocked with trout from the west via Two-Ocean Pass. 



The trout of the great basin of Utah (Lake Bonneville), is descended 

 from the trout of the Upper Snake (lewisi) which is not evidently differ- 

 ent from typical mi/kins ', the fish fauna of Lake Bonneville and the Upper 

 Snake being still virtually identical, the disappearance of the outlet of 

 Lake Boimeville to the north having taken place in times comparatively 

 recent. The trout of the Nevada Basin (Lake Lahontan) is apparently 

 descended from typical mi/kins, the outlet of that lake having entered the 

 Columbia below the Snake River falls, and its disappearance being no 

 doubt of earlier date. The faunas of lakes Bouneville and Lahontan at 

 present have little in common. Almost nothing is known of the Tertiary 

 Lake Idaho, now represented by lakes Malheur, Warner, Goose, etc. 



In any event, whether this hypothetical line of descent be true or not, 

 the fact remains that nowhere in the series can we place an absolute line 

 of separation between Salmo mykiss and Salmo gairdneri, and they approach 

 each other most closely in southeastern California, and in the Middle 

 Columbia. 



We arrange the subspecies in accordance with the above suggestions, 

 leaving each recognizable variation, for the time being, with the title of 

 subspecies. Some of them, as macdonaldi and agua-bonita, may ultimately 

 be ranked as species, on account of their local isolation and consequently 

 better defined characters, while others may prove wholly undefinable. 



It is not unlikely, that when the waters of the Northern Hemisphere 

 are fully explored, it will be found that all the black-spotted tout of 

 America, Europe, and Asia are forms of one species, for which the oldest 

 name is Salmo trutta, Linnaeus. 



The various subspecies or varieties of the Salmo mykiss. group which we 

 are able to distinguish with more or less certainty are given in the follow- 

 ing analysis : 



a. Black spots almost as numerous on the head as on the posterior part of body. (Northwest- 

 ern forms.) 

 6. Scales usually about 160 to 170. 



c. Spots rather large, profusely scattered and irregular, usually none on the belly. 

 d. Ked marks under the dentary bones always present. 



MYKISS; CLAKKII; LEWISI, 779-779b. 



dd. Red marks under dentary bones obsolete or nearly so. GIBBSII, 779c. 



cc. Spots rather large, sparsely scattered, some present on the belly and on lower side 



of head; adult with elongate spots; head slender and conical. Lake Tahoe 



(Basin of Lake Lahontan.) HENSHAWI, 779d- 



bb. Scales larger, usually about 145; spots numerous but rather small. Great Basin (Lake 



Bonneville Basin.) VIRGINALIS, 779e. 



oo. Black spots chiefly placed on the posterior half of body. Red blotch on dentary bones 



conspicuous. (Southwestern forms.) 

 e. Scales not very small, about 160; spots of moderate size. (Rio Grande Basin.) 



8PILURU8, 779f. 



ee. Scales very small, about 180. 



/. Spots rather large ; lower fins distinctly red, rarely orange. 



g. Spots very numerous; a red lateral band. (Colorado Basin.) 



PLEURITICUS, 779g. 

 gg. Spots less numerous, none anteriorly. (Lake Waha, Washington.) 



BOUVIEBI, 779h. 



