Extracted from: Timberlake P.H., (1969). A Contribution to the Systematics of North America Species of Synhalonia (Hymenoptera, Apoidea). University of California Publications in Entomology Volume 57|
Some of the material recorded in the past under the name of acerba or intrudens must have misidentified. An early record of the male of acerba by Cockerell and Fowler's record of the male must have been based on specimens of edwardsii, and Fowler's female of acerba undoubtedly belonged with his albopilosa. Fowler's intrudens, on the other hand, seems to have been the male of actuosa.
Female. Black, clothed with fulvous brown to pale ochreous or whitish pubescence, moderately dense on head and thorax. Hair of abdomen beyond tergite 1 black, with narrow band of white appressed pubescence on apical depression of tergites 3 or 4, that on tergite 3, or both bands, sometimes evanescent. Hair of legs blackish, except on femora. Sometimes hair of head and of sides and underpart of thorax becomes entirely black. Head broader than long, inner orbits slightly converging above. Vertex slightly impressed on each side; lateral ocelli somewhat less than their distance apart from nearest eye, and their diameter from occipital margin. Galeae of proboscis with numerous, rather sparsely set, erect hairs curved over at their tips. Clypeus densely rugoso-punctate. Mesonotum nearly opaque, with close, shallow punctures, but surface nearly concealed by dense pubescence. Abdomen dullish, apical depression of tergites, especially of tergites 1 and 2, more shining; depression of tergite 1 broadly impunctate and hairless across middle, and that of tergite 2 also broad, but thinly hairy, with minute punctures, and more sparsely punctured and hairy on its median third part. Second submarginal cell receiving recurrent nervure about one-fourth of its length from apex. Length 13-14 mm, anterior wing 10 mm, width of abdomen 5.5 mm.
Male.—Black, small joints of tarsi ferruginous. Labrum and clypeus except on lateral margins yellow, clypeal mark wrell separated from margin of eyes, but reaching summit of disk. Pubes¬cence ochreous, or more or less brownish above and on legs. Hair of abdomen mostly long, erect, longer and pale at base, and black on apical margin of tergite 2 and on following segments, sometimes with a little white, especially on each side of tergite 5.
Head broader than long; inner orbits of eyes somewhat convergent above. Vertex strongly impressed on each side, making summit of eyes prominent. Lateral ocelli about their own diameter from occipital margin and one and one-half times their diameter from nearest eye. Galeae of proboscis nearly hairless in comparison with female. Antennae slender, reaching about base of tergite 3, joint 3 about two-thirds as long as 4. Middle tibiae excised beneath on apical half, obtusely angled near middle on anterior side, the angle not at all extended in a ridge across underside. Middle basitarsi narrowed toward apex on apical half, with outer angle of apex sharply but briefly produced. Sternite 6 with narrow, oblique, groove-like impression on each side, and disk with submarginal hair on each side of apex, and short, rather thin, erect hair at base. Parameral lobes of genital armature broad at base, nearly as wide at truncate apex and con¬stricted on middle half, basal half of outer face with close-set erect hair. Length about 13 mm, anterior wing 10 mm.