_Butterfly._--Larger than _C. philodice_. The male is pale canary-yellow, with much narrower black borders than the preceding species. The female is pale yellow or white, without black borders, or, at most, faint traces of them at the apex of the primaries. On the under side the wings are silvery-gray, yellow only at the base and on the inner margin of the primaries. The discal spot on the hind wings is white. Expanse, ♂, 1.85 inch; ♀, 2.10-2.30 inches. _Early Stages._--The caterpillar is uniformly yellowish-green, with a white band on each side, broken with orange-red dashes running through it. The chrysalis, which resembles that of _C. philodice_ in form, is yellowish-green, darkest on the dorsal side, and adorned with three small red dots on the ventral side of the abdomen near the wing-cases. The caterpillar eats _Astragalus_, _Thermopsis_, and white clover. Expanse, ♂, 1.90-2.15 inches; ♀, 2.00-2.30 inches. The species is found in Colorado and the mountain regions to the north and west of that State. (7) =Colias interior=, Scudder, Plate XXXV, Fig. 10, ♂; Fig. 11, ♀ (The Pink-edged Sulphur). _Butterfly._--The male on the upper side closely resembles _C. philodice_, but is smaller, the fringes of the wings rose-colored. The female is pale yellow above, more frequently white, with the tips of the fore wings lightly marked with blackish. On the under side the fore wings at the apex and the entire surface of the hind wings are rusty orange-yellow. The discal spot on the hind wings is silvery, bordered with rosy-red. Expanse, ♂, 1.30-1.75 inch; ♀, 1.60-2.00 inches. _Early Stages._--Little is as yet known of these. The species was first found by Professor Louis Agassiz on the north shore of Lake Superior. It ranges through a rather narrow belt of country, through Quebec, Ontario, and westward to the Rocky Mountains north of the valley of the St. Lawrence and the Great Lakes. (8) =Colias scudderi=, Reakirt, Plate XXXV, Fig. 8, ♂; Fig. 9, ♀ (Scudder's Sulphur). _Butterfly._--The male on the upper side is colored like _C. philodice_, but the black borders are much wider. The fringes are rosy. The female is generally white,--very rarely slightly yellow,--with very pale dark borders, or often without any trace of black on the outer margin of the wings. On the under side the apex of the fore wings and the entire surface of the hind wings are greenish-gray. The discal spot of the secondaries is well silvered and margined with pale red. Expanse, 1.80-2.00 inches. _Early Stages._--We know but little of these, except that the caterpillar feeds on the leaves of the huckleberry and the willow. Scudder's Sulphur is found in Colorado, Utah, Montana, and British Columbia. (9) _Colias pelidne_, Boisduval, Plate XXXV, Fig. 14, ♂; Plate XXXVI, Fig. 15, ♂; Fig. 16, ♀ (The Labrador Sulphur).