76 AMERICAN HYMENOPTERA. 



40. The scutellum and first dorsal abdominal segment clothed with 



entirely yellow pile soiioriis. 



The scutellum usually bearing entirely or mostly black pile and 

 the first dorsal segment usually with considerable black pile 

 on its front portion peiinsylvanious. 



41. The black interalar band more than one-half as wide (from front 



margin to rear margin) as long (from wing base to wing 



base) mertius. 



The black interalar band not more than one-half as wide as long. 



iiicarum n. sp. 



42. Malar space nearly one-fourth as long as the eye ; length, 20 mm. 



to 24 mm mexioaniis. 



Malar space a little more than one-fifth as long as the eye ; length, 

 20 mm. to 21 mm medius. 



43. Dorsum of thorax unicolorous 44. 



Dorsum of thorax bicolored 45. 



44. Pleura black ecuadorius. 



Pleura very pale yellow moutezumse and weisi. 



45. The first two dorsal abdominal segments black 46. 



The first two dorsal abdominal segments yellow 47. 



46. Dorsal abdominal segments four to six, inclusive, clothed with 



white hair robiistus var. liortnlaii.s. 



The fourth dorsal segment yellow and the fifth mostly black. 



triuoiniuatiis. 



47. Pleura yellow nigrodorsalis. 



Pleura black 48. 



48. Dorsal abdominal segments three and four black. 



robnstiis var. steinbaclii. 



Dorsal segment three entirely or mostly yellow ; segment four with 



entirely or mostly white pile robustiis (typical). 



49. Malar space fully as long as its width at apex opifex. 



Malar space not as long as its width at apex sulfuratus. 



Table for Determination of Workers of Bombus 

 South of Northern Boundary of Mexico. 



With only black or black and white pile 1. 



With more or less ferruginous-red, orange, ferruginous, or yellow 

 pile 5- 



1. Entirely black 2. 



With more or less white pile 4. 



2. Malar space somewhat longer than its width at apex kolili. 



Malar space somewhat shorter than its width at apex 3. 



3. Pile very short and coarse brevivillu.s. 



Pile distinctly longer and finer than that of brevivillus niger. 



