260 AMERICAN HYMENOPTERA. 



Third dorsal abdominal segment with a considerable amount of 

 yellow pile especially on apical half 59. 



59. Body rather slender; pile short and dense; western. 



califoviiiciis. 

 Body more robust; pile long and loose; colors (ferruginous, yel- 

 low and black) neither strong nor sharply defined ; northern. 



polaris. 



60. Each of the first two segments of the flagellum of the antenna 



bearing a noticeable tuft of hairs on the outer side. 



mixtiis. 

 These segments without tufts of hair sitkensis. 



61. Basal portion of flagellum of antenna, when viewed laterally, ap- 



pearing strongly crenate below ; fourth antennal segment 



as long as the third ; eastern ternariiis. 



Basal portion of flagellum not appearing strongly crenate when 

 viewed laterally ; third antennal segment slightly longer than 

 fourth ; western 62. 



62. Yellow pile on face and on anterior portion of thorax above 



strongly mixed with black hairs melanopyg-iis. 



Yellow pile on these regions with few or no black hairs intermixed. 



etlwardsii. 



63. Abdomen with some segments bearing ferruginous-red pile 67. 



Abdomen with no segment bearing ferruginous pile 64. 



64. Apical abdominal segments bearing white or whitish ferruginous 



pile occidentalis. 



Apical abdominal segments not bearing white or whitish ferrugin- 

 ous pile 65. 



65. Face nearly covered with yellow pile fernaldi. 



Face without a great amount of yellow pile californicus. 



66. Colors (yellow, ferruginous-red and black) bright and contrasting 



sharply sylvicola. 



Colors (yellow, ferruginous-red and black) dull, not contrasting 

 sharply gelidus. 



67. Front part of dorsum of thorax clouded by a mixture of yellow and 



black hair .melanopygns. 



Dorsum of thorax not so clouded in front liuntii. 



Subgenus BOMBUS Robertson (genus). 

 Bombus Robertson, Trans. Amer. Ent. Soc, XXIX, 1903, p. 176. 

 Viereck et als., Can. Ent., XXXVI, 1904, p. 97. 

 Viereck, Trans. Amer. Ent. Soc, XXXII, 1906, pp. 224 and 



240. 

 Swenk, Ent. News, XVIII, 1907, p. 295. 

 Subgenus Bombus Franklin, Trans. Amer Ent. Soc, XXXVII, 1911, 

 p. 157. 



Type. — Bombus ^Bombus) terrestris (L.). 



