1 86 UNIVERSITY OF COLORADO STUDIES 



D. Pollen-collecting bees with three submarginal cells and a long, filiform tongue, making 

 nests in wood or in stems of plants. XYLOCOP I FORMES. 



i Large robust bees; mostly tropical. XYLOCOPIDAE. 



Xylocopa Latr. (P.) 

 2 Small bees; not rare in temperate regions. CERATINIDAE. 



Ceratina Latr. (P.) 

 SOCIAL BEES: API FORMES 

 Eyes hairy; marginal cell very long. APIDAE. Apis L. (not native in America.) 



Eyes not hairy. BOMBIDAE. 



Pollen-collecting bees. Bombus Fabr. (P.) 



Parasitic bees, the females without polleniferous areas on hind legs; living in 



nests of Bombus. Psithyrus Lepeletier (P.) 1 



The North American bees may be divided into three groups according 



to their supposed origin: 



i Nearctic genera, which have probably inhabited North America dur- 

 ing the larger part of Tertiary time. 



2 Palaearctic genera, which have probably reached North America during 

 the Miocene, or derivatives from such genera. 



3 Neotropical genera and their derivatives, which probably for the most 

 part reached America during the latter part of Tertiary time. 



These are marked N., P. and S., respectively, in the list above. D. 

 signifies an American derivative. 



A few genera, such as Lithurgus and Megachile, were doubtless com- 

 mon to the New and Old Worlds prior to the Miocene invasion. There 

 can be no doubt that Megachile contains elements of Nearctic as well 

 as Palaearctic origin; the truly Palaearctic types are such species as 

 M. melanophaea, M. vidua, etc. 



Robertson's Classification 

 Mr. Charles Robertson, in the Canadian Entomologist, 1904, has 

 given a classification of the groups of Illinois bees, of which the follow- 

 ing is a partial abstract. It is based wholly on the females. Equivalent 

 names in our classification are given within square brackets. 



APYGIDIALIA 



(Sixth abdominal segment exserted, without a pygidial area) 



A. Tongue flat, bilobed; facial foveae present; mandibles bidentate; maxillary palpi 



longer than blade of maxilla. 



1 Two new species of Psithyrus have been collected by Mr. S. A. Rohwer at Eldora, Colorado; they will 

 be published by Mr. H. J. Franklin. One of them extends northward as far as Sitka, Alaska. 



