332 AMERICAN HYMENOPTERA. 



Wings. — About like those of workers. 



Legs. — Coxae, trochanters and femora bearing a large amount of 

 yellow pile, in most cases mainly clothed with it ; fore and middle 

 tibiae mostly black, but with a usually strong posterior fringe of ferru- 

 ginous pile of varying shade ; posterior tibiae with outer faces convex 

 and naked, in some specimens with a few scattered hairs, anterior 

 fringes rather short and posterior ones long, thtis forming the dis- 

 tinct, but weak, corbiculae ; hind metatarsi with rather long posterior 

 fringes. 



Dimensions . — Length : queen, 13 mm. to 17 mm. ; worker, 9 mm. 

 to 12 mm. ; male, 10 mm. to 12 mm. Spread of wings : queen, 31 

 mm. to 35 mm. ; worker, 19 mm. to 31 mm. ; male, 24 mm. to 26 

 mm. Width of abdomen at second segment : queen, 7^ mm. to 9 

 mm. ; worker, 4^ mm. to 7^ mm. ; male, 5 mm. to 6 mm. 



Redescribed from three queens (one of them a homotype 

 of bifarius Cress.), eight workers and eight males. 



Variations. — With the exceptions of rtdocinchis Cress., 

 californicus Smith, occidentalis Greene and plexiralis Nylander 

 this is the most variable species of Bo?nbus in North America. 

 I have had a very large series of specimens and have been 

 able to make out a complete intergradation between the fol- 

 fowing forms, which seem well marked enough to deserve 

 separate description. 



Color Variant 1. — {bifarius Cresson). Queen, typical described 

 above and worker like it. Specimens from Colorado, Utah and New 

 Mexico. 



Color Variajit 2. — {cooleyi Morrill, pars.). Queen and worker like 

 the typical queen, but with the anterior two-thirds of the second dor- 

 sal abdominal.segment entirely covered with black pile and a sharp me- 

 dian v-like projection of the same color extending backward from this 

 across, or nearly across, the third segment ; sides of the posterior por- 

 tion of the second segment and sides of the third segment covered with 

 ferruginous-red or yellowish-ferruginous (of greatly varying shade) 

 pile ; yellow pile on thorax very light, almost white. Numerous speci- 

 mens from Montana and Utah. 



Color Variant 3. -{cooleyi Morrill, pars.). Queen and worker like 

 Color Variant 2, but with second dorsal abdominal segment bearing 

 only a touch of light yellowish-ferruginous pile on the sides of the api- 

 cal portion and with segment three having the anterior half covered 

 with black pile ; mesopleura covered with yellow pile nearly to bases 

 of legs. Several specimens from Montana. 



Color Variant 4. — Queen and worker like Color Variant 3, but with 

 second dorsal segment entirely black and third segment bearing ferru- 



