BEES OF BOULDER COUNTY, COLORADO 255 



3. Very large; anterior wing about loj mm. long; nervures dark; hair on inner side 

 of hind basitarsus black (Boulder, fls. Grindelia, Aug. 7, W. P. CklL; fls. Chryso- 



thamnus, Sept., Rohwer) mizese Ckll. 



Much smaller; nervures ferruginous (Boulder, fls. Grindelia, Aug. 21, Ckll.) 



agilis Cresson 



4. Head extremely broad; hind basitarsus with long white hair on outside, and black 



on inner (Boulder, fls. Opuniia) pallidicincta Ckll. 



Head ordinary 5. 



5. Tuft of hair on tegulse in front black; abdominal bands with a strong orange tint 

 (South Boulder Canyon, fls. Grindelia, Aug. 9, W. P. Ckll.) . grindeliae Ckll. 

 Tuft of hair on tegulae in front Hght : abdominal bands grayish white, or only faintly 

 yellowish (Boulder, fls. Grindelia and sunflower, Aug. 5 to 7, W. P. Ckll.; fls. 

 Chrysothamnus graveolens, Sept. 12, Rohwer) confusiformis Ckll. 



6. Large; about 14 mm. long; antennae red beneath obliqua Say 



Much smaller 7. 



7. Mesothorax with a good deal of black hair; tegulae with a tuft of black hair; 



labrum black grindeliae Ckll. 



Mesothorax without black hair; small species 8. 



8. Labrum (exclusive of its hair) black; mandibles with no yellow spot; length 10 to 

 II mm. (Boulder, fls. Helianthus, Aug. 26, Rohwer) . . agilis semiagilis Ckll. 

 Labrum black, with a very obscure hght spot; spines at sides of last abdominal 

 segment very short; hair of thorax above very pale ochreous; mandibles with a 

 very small yellow spot (Boulder, fls. Grindelia serrulata, Sept. 5, Ckll.) 



agilis Cresson, var. a. 

 Labrum with a large yellow spot; insect rather large, approaching M. menuacha^ 

 hair of thorax above practically white; mandibles with no yellow spot (Boulder, 

 July 29, Ckll., at sunflower, Aug. 7, W. P. Ckll.) . . agilis Cresson, var. b. 



Labrum light except lateral comers; mandibles with a large yellow spot (Boulder, 

 July 29, Ckll., at sunflower, Aug. 7, W. P. Ckll.) . . . agilis Cresson, var. c. 



XENOGLOSSA Smith 

 Thorax with reddish hair; male clypeus black with a large yellow spot; in flowers 

 of Cucurbitaceae pruinosa Say * 



TETRALONIA Spinola 



Females I. 



Males 2. 



1. Hind spur of hind tibia hooked at end (Boulder, S. A. Johnson) dilecta Cresson 

 Hind spur not hooked; abdomen shining black, with only one white hair-band, 

 which is on fourth segment, but a white spot on each side of third acerba Cresson 



2. Hair of thorax above bright rufo-fulvous (Boulder, fls. Astragalus, June, W. P. 



Ckll.) astragalina Ckll. 



Hair of thorax above pale or dull 3. 



3. Very large; the entirely black flagellum at least 11 mm. long (Fort Collins) 



gillettei CkU.* 

 Not so large • 4. 



