ROCKY MOUNTAIN BEES 191 



31 Marginal cell at apex reaching costal margin of wing; females without ventral scopa. 



Halictoides (17) 

 Marginal cell at apex more or less distinctly separated from costa; females with a 

 ventral scopa. 3 2 



32 Females with two large protuberances on middle of face, the space below them smooth 

 and shining; males with the abdomen ending in a point; marginal cell sharply pointed, 

 away from costa (one species, a rather large bee, in our region). Lithurgus (18) 

 Females and males not thus distinguished. 33 



33 Clypeus smooth and shining, emarginate in the middle; a small bee about 8 mm. long; 

 ventral scopa light fulvous or orange (male unknown). 



Titusella pronitens Ckll. (19) 

 Clypeus not thus smooth. 34 



34 No pulvilli on feet; species usually of medium size or large; ventral scopa usually 

 pale (many species). Megachile (25) 

 Pulvilli present. 35 



35 Rather large bees, with a long parallel-sided abdomen; ventral scopa black. 



36 

 Small bees, length 9 mm. or less; ventral scopa pale. 37 



36 Male with face largely silvery from appressed hairs, and clypeus shallowly emarginate; 

 females with eyes slightly converging above. Monumetha (21) 

 Male unknown; females with eyes diverging above; clypeus with a strong, smooth 

 and shining, longitudinal median ridge. Osmia hypocrita Ckll. 



37 Base of first abdominal segment ordinary, rounded, with a narrow longitudinal sulcus. 



38 

 Base of first abdominal segment with a flattened or concave smooth shining plate or 

 basin, the edge of which is well defined. 39 



38 Male with flagellum greatly thickened, with a terminal hook. Alcidamea (20) 

 Male with flagellum long and filiform (genus not yet found in Colorado). 



Robertsonella (22) 



39 More coarsely punctured; end of first recurrent nervure not more (usually less) distant 

 from base of second submarginal cell than half length of first transverso-cubital; male 

 abdomen not ending in four teeth. 4° 



Less coarsely punctured; end of the first recurrent nervure more distant from base of 

 second submarginal cell than half length of first transverso-cubital; male abdomen 

 ending in four teeth. 4 1 



40 Anterior legs largely red (Boulder, at flowers of Mvnarda, July 16, 1908, W. P. Cock- 

 erell). - Heriades asteris Ckll. 

 Legs all black (Boulder, July, W. P. Cockerell, S. A. Rohwer). 



Heriades carinatus Cresson (24) 



41 Larger, anterior wings 4I to 5^ mm. (Boulder, August 28, Rohwer; Rifle, Colo., 

 July, Rohwer; usually taken at flowers of Grindelia). 



Ashmeadiella denticulata Cresson (23) 

 Smaller, anterior wings about 3 mm. (Boulder, May, Rohwer). 



Ashmeadiella prosopidis Ckll 



