208 AMERICAN HYMENOPTERA. 



3. Tricolorous. These are as follows : 



(&) black, yellow and ferruginous (e. g. — huntii, pule her). 



(b) black, yellow and white (e. g. — appositus, robustus). 



(c) black, cinereous and white (e. g. — volucelloides). 



(d) black, ferruginous and white (e. g. — eoeeineus) . 



(e) cinereous, ferruginous and brown (e. g. — hattdlirschi) . 



4. Quadricolorous. Very few species, the colors being : 



(a) black, yellow, ferruginous and white (e. g. — sulfuratus). 



(b) black, white, ferruginous and cinereous (e. g. — butteli). 



Of the New World species, the largest number are tri- 

 colorous and, of these tricolorous forms, the "black, yellow 

 and ferruginous " ones outnumber all the others by more 

 than two to one. Next in numbers to the "black, yellow 

 and ferruginous " species are the "black and yellow" ones 

 of the bicolorous series, these outnumbering by two to one 

 all the others of that series. The coloration of the male is, 

 in some species, strikingly different from that of the females 

 and, in Bombus, there is also sometimes a considerable dif- 

 ference in this respect between the worker and the queen. 



Head (fig. 53). 



The hypognathous head is of good length and thickness, 

 but is rather narrow in comparison with that of most other 

 bee families. Its usual form might, perhaps, be best de- 

 scribed as sub-triangular. There is, however, great varia- 

 tion in its shape among the various species, it being rather 

 strongly rotund in some, while in others it is elongate tri- 

 angular. This varying shape of the head is of considerable 

 value in classification, especially as, within each natural 

 group of species, it is more or less constant and character- 

 istic. In profile, the head appears somewhat convex in front. 



The different sclerites forming the head are so completely 

 fused as to be indistinguishable, and we can therefore desig- 

 nate the regions of the head only in a general way. The 

 occiput is, in this paper, considered to extend from the neck 

 (junction of head with pronotum) up and over the occipital 

 ridge and forward to the supra-orbital line (the line tangent 

 to the extreme upper ends of the eyes. It is shorter in some 

 species than in others because of the greater upward exten- 

 sion of the eyes in all castes of those species. 



