242 UNIVERSITY OF COLORADO STUDIES 



5. Large, fully 11 mm. long; abdominal hair-bands on apices of segments; third 

 submarginal cell twice as broad as second (Boulder, fls. Pulsatilla; G. Weston, 



E. Bethel, T. &» W. Ckll.) lerouxii Lep. 



Smaller; hair bands wholly or mainly on bases of abdominal segments 6. 



6. Wings clear, almost milky, large for size of insect; stigma amber color (Boulder, 



April 30, T. fir* W. Ckll.) aberrans Crawford 



Wings smoky ?• 



7. Larger; not shining (Boulder, fls. Salix, Harry House) . . trizonatus Cresson 

 Smaller; shining (Florissant) COOleyi Crawford * 



8. Abdomen broad, the hind margins of the segments with hair-bands; third sub- 

 marginal cell more than twice as broad as second 9. 



Abdomen not thus banded; third submarginal cell not so large in proportion to 

 second 10. 



9. Larger, abdominal bands very dense; head and thorax brassy-green (Boulder, 



fls. Claytonia lanceolata) arapahontun Ckll. 



Smaller, abdominal bands usually less dense; head and thorax blue-green (Boulder, 

 fls. Phacelia, Claytonia lanceolata) meliloti Ckll. 



10. Abdomen amber-color (Florissant) scrophulariae Ckll.* 



Abdomen black il. 



Abdomen green or blue 12. 



11. Smaller; area of metathorax with very fine deHcate striae on basal part (Halfway 

 House, Pikes Peak, Sept., Ckll., also Florissant) .... niidosensis Ckll.* 

 Larger; area of metathorax with coarse strong ridges (Gregory Canyon, Apr. 16, 

 fls. Pulsatilla hirsutissima) cressonii Robertson 



12. Hair of abdomen, covering segments 3 to 5, pale ochraceous (Boulder, fls. Pulsatilla 



hirsutissima, May i, Marie Gill) pilosus Smith, var. 



Hair of abdomen white 13- 



13. Head oval, face comparatively narrow (Boulder, fls. Senecio, May 17, W. P. Ckll.) 



pruinosus Robertson 

 Head round, face comparatively broad (Boulder, fls. Odostemon, April 6, W. P. 



Ckll.) pruinosiformis Crawford 



The following table, adapted from Crawford, will facilitate the determination of 

 certain males. 



Species without any green i. 



Species with more or less green; wings and nerwires dark . cressonii Robertson 



1. Face and legs entirely dark sisymbrii Ckll. 



Face and legs not entirely dark 2. 



2. Species wth hair-bands on the apical margins of abdominal segments . 3. 

 Species wthout such hair-bands 4- 



3. Flagellum bright ferruginous beneath armaticeps Cresson 



Flagellum darker beneath lerouxii Lep. 



4. Tibiae entirely dark trizonatus Cresson 



Tibia: not entirely dark cooleyi Crawford* 



Mr. Crawford informs me that H. colatus Vachal, described from Colorado, is a 

 male trizonatus. 



