It seems probable that the American trout originated in Asia, extended its range to southeast Alaska, thence southward to the Fraser and Columbia, thence to the Yellowstone and the Missouri _via_ Two-Ocean Pass; from the Snake River to the Great Basins of Utah and Nevada; from the Missouri southward to the Platte and the Arkansas, thence from the Platte to the Rio Grande and the Colorado, and then from Oregon southward coastwise and along the Sierras to northern Mexico, thence northward and coastwise, the sea-running forms passing from stream to stream. [Illustration: FIG. 61.—Rainbow Trout (male), _Salmo irideus shasta_ Jordan. (Photograph by Cloudsley Rutter.) ] Of the American species the rainbow trout of California (_Salmo irideus_) most nearly approaches the European _Salmo fario_. It has the scales comparatively large, although rather smaller than in _Salmo fario_, the usual number in a longitudinal series being about 135. The mouth is smaller than in other American trout; the maxillary, except in old males, rarely extending beyond the eye. The caudal fin is well forked, becoming in very old fishes more nearly truncate. The head is relatively large, about four times in the total length. The size of the head forms the best distinctive character. The color, as in all the other species, is bluish, the sides silvery in the males, with a red lateral band, and reddish and dusky blotches. The head, back, and upper fins are sprinkled with round black spots, which are very variable in number, those on the dorsal usually in about nine rows. In specimens taken in the sea this species, like most other trout in similar conditions, is bright silvery, and sometimes immaculate. This species is especially characteristic of the waters of California. It abounds in every clear brook, from the Mexican line northward to Mount Shasta, or beyond, the species passing in the Columbia region by degrees into the species or form known as _Salmo masoni_, the Oregon rainbow trout, a small rainbow trout common in the forest streams of Oregon, with smaller mouth and fewer spots on the dorsal. No true rainbow trout have been anywhere obtained to the eastward of the Cascade Range or of the Sierra Nevada, except as artificially planted in the Truckee River. The species varies much in size; specimens from northern California often reach a weight of six pounds, while in the streams above Tia Juana in Lower California the southernmost locality from which I have obtained trout, they seldom exceed a length of six inches. Although not usually an anadromous species, the rainbow trout frequently moves about in the rivers, and it often enters the sea, large sea-run specimens being often taken for steelheads. Several attempts have been made to introduce it in Eastern streams, but it appears to seek the sea when it is lost. It is apparently more hardy and less greedy than the American charr, or brook-trout (_Salvelinus fontinalis_). On the other hand, it is