There will hardly be a naturalist who has not spent considerable time to study the questions–What is a genus, and what are generic characters? Indeed, work is nearly impossible without having taken a position with regard to these questions. A full record of the literature, even the most condensed one, would be here out of p1ace, but I have been induced by a recent and most surprising discovery bearing upon this question to make this communication.

Fore wings whitish yellow and olive brown. The median field whitish yellow except a costal blotch of the darker tint. Base narrowly whitish yellow, succeeded by an oblique olive: brown band. The outer line bordering the median space is nearly upright, a little irregular and slightly notched opposite the cell and again at internal margin. It is followed by the broad olive brown subterminal space. The subterminal line is yellowish, brought near the margin, flexuous, and the veinlets on the terminal space are marked with yellowish.

The species described in this paper are from Mendocino. The genus seems to be more numerously represented on the West than on the East Coast of North America. Some of the new forms resemble the Eutopean. To none of these species can I refer Dr. Boisduval's descriptions of hectoides or californicus.

Palpi with the outer suface of the second joint dark bluish brown or blackish, dusted sparsely with white, the inner surface being white dusted with blackish scales; third joint blackish. Head and tongue white, the vertex with a faint purplish tinge, and dusted with dark brown. Thorax very pale ochreous and white, dusted with blackish scales, and with the anterior margin shining black.

Basal joints of fore legs ochreous red; femora and tibia dark brown, obscurely marked with white; tarsi white dusted and annulate with brown. Intermediate legs like the first pair, except that the basal joints are brown. Intermediate legs like the first pair,except that the basal joints are brown; hind legs and the under surfaceof the abdomen white dusted with dark brown, the tarsi tinged with yellowish and the upper surface of the abdomen brownish.

On the 14th May last I found several eggs of archippus on milk weed. These hatched on the 17th inst. on the 19th all had passed first moult. on the 21st all had passed second moult. Onthe 22nd two passed third moult. On the 25th these two passed fourth moult, and were one inch long. They continued to grow till the 29th, when they measured 1.8 inch, and in the morning had fixed for chrysalis.