Il.—Specific Characters in the Bee Genus Colletes 
BY MYRON HARMON SWENK 
Five years ago the writer began the accumulation of material 
in this genus with the intention of ultimately monographing the 
North American species. The choice was determined partly for 
the reason that the collection of the University of Nebraska con- 
tained an excellent nucleus of material for such a study, and 
partly because almost nothing had been done either in Europe or 
America to enable the determination of the species, which, except 
for a few tables accompanying local lists, were known chiefly 
from isolated and mostly unsatisfactory descriptions. In fact, 
the genus had been practically ignored by systematic hymenop- 
terists. Work had not proceeded far, however, before it became 
apparent that the task was beset with unusual difficulties. The 
lack of well-marked structural characters throughout the genus 
had led authors to emphasize the coloration and arrangement of 
the pubescence and other equally variable features as criteria of 
specific distinctness, while the more stable differences in sculpture 
and proportion of parts were largely passed over. This made the 
recognition of species from their original descriptions a matter 
of considerable uncertainty and always of great difficulty, and, 
combined with the paucity of reliably named material in collec- 
tions, caused the work of revision to progress very slowly. But 
through the generosity of Messrs. Cockerell, Robertson, Viereck, 
and several other of our hymenopterists in sending certain au- 
thentically named specimens from their collections, and in kindly 
comparing with the types in their care material tentatively deter- 
mined by the writer, a collection of reliably named specimens has 
been gradually built up which can form the basis of a preliminary 
revision. In the present paper all the species, twenty-six in num- 
ber, possessing black thoracic hairs, at least in the female, are 
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