Couplet 1. See Section 19 for illustrations ofvariation in these characters. Some L-T bees do not agree with the statement on the labial palpus. In some subgenera of Chelostoma (a small, slender, holarctic megachilid), the third segment (as well as the first two) is broad; it is rather rigidly attached to the second, only one segment being nonflattened. In certain African and Malagasy social parasites in the Allodapini, the last two segments of the labial palpus do not contrast with the first two, as they do in most L-T bees; in one genus, Effractapis, the labial palpus has only three segments.
S-T bees rarely have more than the normal four segments of the labial palpus; extra segments are known in three palearctic species of Andrena (Andreninae) and three species of South American Leioproctus (Colletinae) (see Sec. 39). A stipital comb and associated concavity occur in the central Asian Eremaphanta (Dasypodainae), as in L-T bees. The few S-T bees in which the first two segments of the labial palpus are elongate include the Brazilian Protomeliturga (Panurginae) and the North American Andrena (Callandrena) micheneriana LaBerge (Andren-inae).
Couplet 2. On the hind legs of female Fideliini (Africa, Chile), long hair suggests a scopa, but pollen is carried only on the metasomal scopa. And in the South African Aspidosmia (Anthidiini) the hind tibia bears long hairs not only suggestive of a scopa but carrying pollen in museum specimens.
In the Apidae the labrum is ordinarily little, if at all, longer than broad, but in some pasitine Nomadinae, parasitic bees without a scopa, mostly small, the labrum is much longer than broad.
Couplet 3. The hylaeine genera whose males have a pointed glossa are Meroglossa, Palaeorhiza, and Hemi-rhiza, all found in Australia and the New Guinea region. Like other Hylaeinae and unlike the families that run to 4 in this couplet, these three genera lack scopal hairs (the scopa is also absent in parasitic Halictidae) and have hairless, groovelike facial foveae.
Couplets 5 and 6. The only bees having two suban-tennal sutures below each antenna, such that the sutures are well separated at their lower ends, are in the An-drenidae (including Oxaeinae). A few other bees, e.g., the Stenotritidae, have two subantennal sutures on each side, but the sutures meet or nearly meet at their lower ends, producing a triangular subantennal area. In the Chilean Euherbstia (Andreninae) these sutures approach one another, leaving the margin of the subantennal area on the clypeus short, and in the Brazilian Chaeturginus (Pa-nurginae) the subantennal sutures on each side nearly meet at the upper clypeal margin, but the subantennal area is long, over three times as long as wide, not a short triangle as in the stenotritids. A few Panurginae (Mexican and Arizona species of Protandrena s. l. and a Brazilian species of Chaeturginus) have only one subantennal suture on each side. Such forms differ from Melittidae in the yellow or white facial areas in the male, the truncate marginal cell, and the presence of facial foveae.
Unfortunately, subantennal sutures are easily seen only when the background is yellow or white. When the face is black, as in nearly all females and many males, these sutures are inconspicuous, often requiring removal of hairs if they are to be seen, and may be impossible to see if the surface is coarsely punctate.
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