Reprinted with permission from the University of Nebraska State Museum from:
Ribble, D. W. 1968. Revisions of two subgenera of Andrena, Micrandrena Ashmead and Derandrena new subgenus (Hymenoptera: Apoidea). Bulletin of the University of Nebraska State Museum 8: 1-124.
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The distinctive characteristics common to primulifrons and trapezoidea are discussed under the latter species. Males of primulifrons can be easily separated from trapezoidea by their short, dull antennae; the male antennae of trapezoidea are longer and shiny. The terminalia of the two species are also different (see description). In both sexes of primulifrons the basal part of the clypeus is usually weakly shagreened, while trapezoidea has coarser shagreening, however, some specimens of primulifrons are like trapezoidea in this respect (see Variation). The female of primulifrons can be distinguished by the short moss-like hairs on the dorsum of the thorax and by the dark brown abdominal terga with close hairs on the medium part, giving the terga a dusty appearance. Female primulifrons lack a distinct tooth on the tarsal claws (see Variation). In trapezoidea the thorax has longer hairs and the abdominal terga are black or very dark brown with bluish-black reflections; the tergal hairs are further apart, giving the terga only a slightly dusty appearance. The tarsal claws are distinctly toothed.
The descriptions below are based mainly on a male and a female from Palo Duro Canyon State Park, Randall County, Texas (April 8, 1963, R. B. Roberts and M. G. Naumann). A total of 470 other specimens of primulifrons were examined during this study.
FEMALE. MEASUREMENTS AND RATIOS. — Length, 6.7 mm; width of mesothorax, 1.9 mm; wing length from tegula, 4.9 mm; facial length/width, 1.04; foveal length/width, 4.25.
INTEGUMENTAL COLOR. — Black to dark brown except: head and thorax with slight bluish-black reflections, thorax with some golden reflections; flagellum orange-brown below; tegula amber; terga with broad amber apices; sterna with narrower amber apices; color otherwise as in piperi.
STRUCTURE. — Sculpturing in general finer over entire body than in piperi. Head otherwise as in piperi except: scape reaching to one ocellar distance from middle ocellus, nearly as long as flagellar segments 1-5; inner eye margins nearly parallel below; maxillary palpus with segments in ratio of about 1.1:1.6:1.3:1.3:1.0:1.1; labial palpus with segments in ratio of about 1.8:1.0:1.0:1.2; labral process asymmetrical (see Variation); clypeus very shiny, shagreening weak basally, center of clypeus without shagreening; genal area in side view slightly wider than eye; facial fovea just barely reaching upper eye margin.
Mesosoma as in piperi except: mesoscutum with distinct punctures, reticular shagreening absent in center of sclerite, parapsidal lines indistinct; metanotal surface much more coarsely sculptured than mesoscutal; posterior and dorsolateral areas of propodeum not raised above enclosure, punctures indistinct, shagreening less granular than on enclosure; mesepisternum with surface having coarser shagreening than on mesoscutal; middle and hind basitarsi widened; hind tibia broadened, tibia one-fourth wider than basitarsus; tarsal 'claws with tooth on inner margin minute; posterior spur of hind tibia much longer than anterior spur; pterostigma medium-sized, twice as wide as prestigma; first transverse cubital vein ending several vein widths from pterostigma.
Metasoma as in piperi except: terga very shiny, punctures distinct, shagreening absent or very weak; sterna with larger punctures than piperi.
VESTITURE. — Hairs as in piperi except: hairs on dorsum of thorax short, but not as short or as close as piperi, moss-like appearance less noticeable; tarsal hairs white; tergum 1 nearly bare; terga 2-4 hairs {except apical fasciae) short, plumose, abdomen with dusty appearance less marked than piperi; apical fasciae interrupted medially on tergum 2, complete on 3 and 4; tibial scopal hairs short, anterior-most weakly curved posteriorly.
MALE. MEASUREMENTS AND RATIOS. — Length, 5.5 mm; width of mesothorax, 1.7 mm; wing length from tegula, 4.4 mm; facial length/width, 0.96; flagellar segment 1/segment 2, 1.55.
INTEGUMENTAL COLOR. — Black to dark brown except: body with slight bluish-black reflections; clypeus and parocular areas cream-colored; flagellum orange-brown below; color otherwise as in piperi.
STRUCTURE. — Sculpturing in general finer over entire body than in piperi. Head otherwise as in piperi except: scape reaching to within less than one ocellar distance of medium ocellus, much longer than flagellar segments 1-3; segment 1 half again as long as 2, slightly longer than 3; segment 2 and 3 tapered toward bases; middle segments broader than long; ultimate segment half again as long as broad; maxillary palpus with segments in ratio of about 1.0:1.7:1.3:1.3:1.0:1.5, apical segment round in cross-section; labial palpus with segments in ratio of about 2.2:1.0:1.2:1.5; labrum two and one-half times as wide as long; clypeus impunctate in center, shagreening weak, in center shagreening absent; genal area in side view slightly narrower than eye.
Mesosoma as in primulifrons female except: metepisternum weakly shagreened, very shiny below, sculpturing much finer than on lateral surface of propodeum; basitarsi and hind tibia unmodified; tarsal claws with large tooth on inner margin.
Exposed metasoma sculptured as in primulifrons female; otherwise metasoma as in piperi.
Hidden sterna and genital capsule very similar to trapezoidea except: sternum 7 with apical lobes further apart; sternum 8 with shaft less abruptly expanded into basal plate; gonocoxite with middle part of gonoforceps more expanded on inner margin, dorsal lobes broader (see trapezoidea, figs. 85-87).
VESTITURE. — Hairs as in piperi.
VARIATION. — The clypeus in both sexes is usually weakly shagreened basally, but in some specimens the shagreening is similar to trapezoidea. Specimens of primulifrons and trapezoidea collected together may have the similar clypeal sculpturing. The shape of the labral process is quite variable in the female of primulifrons, but tends to be a moderately large, symmetrical, rounded lobe. Often the tooth on the inner margin of the tarsal claws in the female appears to be completely absent; when present, the tooth is minute.
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