158 ILLINOIS ACADEMY OF SCIENCE 



expanded form the names and information sent him by 

 Jiirine. It is Juiiue, then, who is responsible for Bremus 

 and for certain other genera not considered in this paper. 

 Bremus included both the true bumblebees and their 

 bumblebee-like inquilines; hence the name Psithyrus of 

 Lepeletier (1832) for these bumblebee-like inquilines still 

 stands. 



The writer has deemed it best, at least for the present, to 

 follow Dr. Franklin and regard Bomhias of Eobertson 

 (1903) as a subgenus instead of as a distinct genus. Fu- 

 ture life history studies of the bumblebees may show that 

 Bomhias is really a valid genus. In a recent article 

 (Frisou, 1D17) it has already been shown that the life his- 

 tory of B. (Bomhias) aiiricomus Robt. differs widely from 

 that of any other true Bremus with which I am familiar. 

 It is thought best, however, at this time to wait until more 

 work has been done on the life histories of our American 

 bumblebees, before using such evidence as an aid towards 

 a natural grouping of the Brcmidae. 



Because of the variation in the color of the i)ubescence 

 of certain species of bumblebees, it has been found neces- 

 sary to put such variable species in the keys in more than 

 one place. There are several varieties of B. riifocinctus 

 Cress, that have not been included in the keys, as they 

 have only been reported from the Rocky Mountain region. 



The males of the two genera of Bremidae may be easily 

 separated from each other by the fact that the volsella and 

 the squama of the genitalia of Psithyrus are membranous, 

 whereas in Bremus they are corneous. 



The outer surfaces of the hind tibiae are usually more or 

 less covered with hairs in the males of Psithyrus^ and in 

 Bremus rather bare. 



In the females, the outer surfaces of the hind tibiae of 

 Psithyrus are more covered with hairs and rounded, while 

 those of Bremus are more bare and flattened. In Psithyrus 

 there are no workers. 



The distribution of the Illinois species of bumblebees is 

 interesting, in that Illinois represents what one might 

 term an intermediate position. Illinois is intermediate 

 between those states possessing the largest and those with 



