254 UNIVERSITY OF COLORADO STUDIES 



Abdomen narrower, oblong, shiny; hair of mesothorax largely or mainly black 

 (Ward, Boulder, fls. Phacelia, Grindelia) vidixa Smith 



7. Small, length not over 11 mm. (Boulder, fls. Phacelia, W. P. Ckll.) . brevis Say 

 Larger, length 12 mm. or more 8. 



8. Middle of clypeus with feeble, sparse pvmctures (Boulder, W. P. Ckll., July 3, fls. 



Opuntia) opuntiarum Ckll. 



Middle of clypeus with strong punctures 9. 



9. Smaller; abdomen oblong, rather narrow; middle tarsi slender (Boulder, fls. 



Argemone intermedia, Aug. 27, Ckll.) montivaga Cresson 



Larger; abdomen broad; middle tarsi broadened 10. 



10. Larger and broader, width of abdomen 5 J mm.; pubescence white or grayish- 

 white (Boulder, W. P. Ckll., Aug. 6 to 9, fls. sunflower) . sezdentata Robertson 

 Smaller, not so broad, width of abdomen about 4 J mm.; pubescence with a yellow- 

 ish tint (Boulder, flis. Grindelia, Aug. 21, Ckll) .... manifesta Cresson 



u. Abdomen without bands, hair on basal 2-2 J segments pale yellowish, beyond that 



black 12. 



Abdomen with evident narrow hair-bands 13. 



12. Spurs of hind tibiae ferruginous; vertex more closely punctured . wootoni Ckll. 

 Spurs of hind tibiae piceous; vertex less closely piinctured wootoiii]calogaster Ckll. 



13. Front tarsi simple I4- 



Front tarsi flattened or excavated 16. 



14. Spines on anterior coxae reduced to short teeth or dentiform angles 



montivaga Cresson 

 Spines on anterior coxae well developed 15. 



15. Mandibles 4-dentate, middle tooth notched .... seidentata Robertson 

 Mandibles 3-dentate brevis Say 



16. End of abdomen (keel of sixth segment) with a very large deep notch; hair of face 

 yellow; anterior femur with an obhque keel near apex on outer side . vidua Smith 

 End of abdomen (keel of sixth segment) notched; hair of face cream-color; ante- 

 rior femur without a subapical keel; middle femur greatly swollen latimanus Say 

 Keel of sixth segment Uttle or not notched; anterior tarsus with a boat-shaped 

 scale or process 17- 



1 7. Spines of anterior coxae slender; keel of sixth segment (seen in lateral view) directed 



caudad pugnata Say 



Spines of anterior coxae broad and flattened; keel of sixth segment jagged, and 

 directed downward manifesta Cresson 



MELISSODES LatreiUe 



Females I- 



Males; clypeus yellow 6. 



1. Very large; anterior part of mesothorax with red hair, posterior part with black, 

 the colors contrasting (Boulder, Aug., fls. sunflower, W. P. Ckll., Rohwer) 



obliqua Say 

 Colors on mesothorax different, at least not red in front 2. 



2. Scutellum without black hair 3. 



Scutellum with hair at least partly black 4. 



