Lewis and Clark were both remarkable for clear and correct descriptions of the animals and plants met with during their journey, many of which were new to science; but as they neglected to give them scientific names, others have reaped the honors of many of their discoveries. I published my identification of the fish in question as being undoubtedly the grayling, and soon afterward received a letter from Dr. Coues, congratulating me and indorsing my opinion, which he said was certainly correct. The Montana grayling is found only in the tributaries of the Missouri River above the Great Falls. In Sheep and Tenderfoot creeks, tributaries of Smith River, in the Little Belt Mountains, it is fairly abundant, as it is likewise in the three forks of the Missouri,--the Gallatin, Madison, and Jefferson rivers. Its ideal home is in several tributaries at the head of Red Rock Lake, swift gravelly streams, and especially in the upper reaches of the Madison above the upper cañon, where the water is rapid, though unbroken, the bottom being dark obsidian sand, with a succession of pools and shallows. I have taken fish weighing two pounds in Beaver Creek, in the upper cañon, which is also an ideal stream. Such situations are peculiarly adapted to the grayling, being preferred to the broken water of rocky streams so much favored by trout. The Montana grayling is a trimmer-built fish than its Michigan cousin, being not quite so deep, proportionally, and with larger scales. Its dorsal fin is about the same height, but with one or two less rays. Its back is gray, with purplish reflections; sides lighter, with lilac, pink, and silvery reflections; belly pearly white. It has a few irregularly-shaped black spots on the anterior part of the body, but none posteriorly as sometimes on the Michigan grayling. It has two oblong dark blotches in the cleft of the lower jaw, and a heavy dark line running from the ventrals to the pectoral fin; these markings are more pronounced in the male, being quite faint or wanting in the female. The dorsal fin has a rosy-red border, six or seven rows of roseate, roundish spots, ocellated with white, and gray blotches form lines between the rows of red spots; in the upper, posterior angle of the dorsal fin are several larger oblong rosy spots; the ventral fins have three rose-colored stripes along the rays; the pectoral and anal fins are plain; the caudal fin is forked.