128 AMERICAN HYMENOPTERA. 



their somewhat shorter malar space and by the hind margin 

 of their posterior metatarsi rather more suddenly arcuate 

 near the base. The males may be separated from those of 

 mexicanus by the differences in the structure of their geni- 

 talia, particularly of the squamae, and by the ferruginous 

 pile on their last dorsal abdominal segment. The genitalia 

 of ynedius may be separated from those of pidlahcs by the 

 somewhat narrower apices of their volsellas, with their some- 

 what less hood-like apical projections, and by the distinctly 

 serrate outer margins of the heads of their sagittae. 



Pullatus, medius and mexicamis all agree in having the tips 

 of the volsellae of their genitalia extend considerably beyond 

 the squamae and far beyond the heads of the sagittae. In 

 this respect, these species all differ markedly from atratus. 



The yellow pile on the specimens of inediiis before me 

 varies from pale straw color to a good deep yellow. 



It seems possible that medius may even grade into a com- 

 pletely black form, and I do not feel certain that ntger, which 

 seems very closely related, is not, in reality, such a gradation 

 of this species. 



Boinbus (Bonibus) mexicanus Cress. 

 Bombus mexicanus Cresson, Proc. Acad. Nat. Sc. Phila., 1878, p. 

 187, 9 S . 

 ? " unifasciatus Smith, Descr. New Spec. Hym., 1879, p. 133, n. 

 8, 9 a d^. 

 " mexicanus Cresson, Trans. Amer. Ent. Soc, VII, 1879, p. 

 231 (Catal.). 

 ? " Cayennensis va.v. Mexicanus Ant. Handlirsch, Ann. Naturh. 

 Hofmus. Wien., Ill, 1888, p. 241, 9 S . 

 " sp. Ant. Handlirsch, Ann. Naturh. Hofmus. Wien., VI, 

 1891, p. 453, d', and perhaps the S . 

 mexicanus Dalla Torre, Cat. Hym., X, 1896, p. 534. 



Cockerell, Cat. Abej. de Mexico, 1899, p. 19 

 (Catal.). 



Types. — Some, at least, of the specimens, from which 

 Cresson made his original description of this species, are in 

 the collection of the American Entomological Society. They 

 came from Mexico. Col. C T. Bingham failed to locate 

 Smith's type specimens of tmifasciatus, in the collection of 

 the British Museum, for me. 



