The nesting habits of many of our wild bees still remain unknown. Their importance, from an ecological as well as from an animal behavior standpoint, is great. Each species is adjusted to a set of environmental conditions which the kind and location of the nest helps to assure it. The young are protected from extremes of heat and moisture, as well as from parasites and predators by the materials composing the cell, by the manner of its construction and by the nesting site selected by the mother bee. The following account consists of brief notes on the habits of certain western species.

In the middle of June, 1934, while spending a few days at Annapolis Royal. N. S., I collected some Haploptilia cases of the pruniella type from the foliage of Kalvnia. Half a dozen or so of these cases were attached to the upper-side of the previous year's leaves; they were dull gray-brown in color and the apical portion was noticeably weather-worn as if the cases had hibernated; there was no sign that living larvae were within them as they remained perfectly quiescent on the leaves. A few other cases, found at the same time, showed evidence that living larvae were still within; these cases were brighter brown in color and appeared to have been more recently constructed as the apical portions showed clearly the smaller cases of one, and sonletimes two, previous instars, attached in the usual holster-like manner to the much larger and broader basal portion. These latter larvae crawled about in the receptacle and fed slightly but soon in their turn became quiescent. The accompanying figures give some idea of the two forms of cases.

In the following paper descriptions are presented for three apparently undescribed species of Arctocorixa. Notes are included on some additional species and a redescription presented for Corisella tumida (Uhler).

Arctocorixa bicoloripennis n. sp.

Male.—Length 5.75 mm. Form and color pattern simulating A. penniensis Hungfd. but size a little smaller. Head short, vertex from above broadly arcuate continuous with margin of eyes. Width of vertex posteriorly between eyes equal to its median length. Face with a weak concavity extending dorsally slightly beyond lower margin of eyes and with greatest width distinctly less than interocular space. Inner margins of eyes only very slightly diverging ventrally. Post-ocular space narrow. Head with a few fine punctures and a few fine pale hairs, surface minutely coriaceous, shining. Antennae with apical segment slender, two-thirds as long as subapical segment.

Walsingham described this species from a variable series of specimens taken in Colusa, Shasta and Siskiyou Cos., Calif. No definite type is designated but from correspondence with Mr. W. H. T. Tams of the ,British Museum I find that the author marked his types "Type I" and "Type II." Type I, the obvious holotype, is labelled "Pit River, Shasta Co. California, VII, 1871, P1. 2, fig. 13" and according to Mr. Tams is much the tawnier of the two "types." Type II is labelled "Uncle Sam Mount, Lake Co. Calif. VI, 1871, PI. 2, fig. 14" and, as the figure shows, is a pale, immaculate form. Barnes and Lindsey make californica Grin. (1908, Can. Ent. XL,, 321) from S. Calif. a synonym and describe the color of the forewings as creamy-white to tawny-brown, the latter color being that given by Grinnell in his description of californica.