398 O. E. PLATH. 



shortly after this revision had appeared in print, Sladen ('12, 

 pp. 274-275) discovered that the character on the basis of which 

 he had established the Pollen- primers is not a dependable one 

 and hence inserted the following paragraph among his "Addi- 

 tional Notes": "B. latreillellus was considered to be a pollen- 

 primer because pollen was found under the eggs in a nest in an 

 advanced stage examined in 1911. But in a nest in an earlier 

 stage kept under observation in 1912 the eggs were laid in cells 

 that contained no pollen, although in at least one case pollen was 

 put into the cell and removed before the eggs were laid. Should 

 future investigation show that latreillellus is a pollen-primer 

 only under abnormal conditions, a better name for the group, 

 consisting or ruderatus, hortorum, latreillellus and distinguendus , 

 would be 'Long-faced Humble-bees'; the term 'pollen-primers' 

 could then be restricted to ruderalus and hortorum. Latreillellus 

 and distinguendus are not closely related to ruderatus and hor- 

 torum." 



For several summers the present writer has devoted most of 

 his time to the study of the biology of bumblebees, and has had 

 occasion to examine the nests of about 200 Bremus colonies be- 

 longing to the following North American species: affinis, ameri- 

 canorum, bimaculatus, fervidus, impatiens, per plexus, occidentalis, 

 separatus, ternarius, terricola, and vagans. This material fur- 

 nished an excellent opportunity to test the soundness of Sladen's 

 ('99 and '12) classification, as applied to four of our seven 

 American groups. The results of this investigation show that 

 Sladen's ('99 and '12) classification provides an excellent basis 

 for further taxonomic and phylogenetic work, but that certain 

 details of his scheme will have to be modified. 



As already stated, Sladen ('12) divides the English Bremidae 

 into two main groups, the Pollen- storers and the Pocket-makers. 

 In regard to the last-named group Sladen ('12, p. 44) says: 

 ' When the usual receptacles for pollen employed by a particular 

 species are not available, it may adopt those employed by others. 

 Thus in a strong nest of B. agrorum, one of the pocket-making 

 species that I had under observation in 1910, the workers, during 

 a period when there were no growing larvae and consequently 

 no pockets for pollen, dropped all the pollen they brought home 



