Studies of North American Bees 6i 



dropped out of the literature. But a comparison of Smith's 

 description with specimens of vincta ^ and with the descriptions 

 of affabilis J* convinces the writer that Cresson was in error in 

 considering piilchella as a synonym of either vincta or affabilis. 

 In the first place both of these species are much too large, being 

 usually lO or ii mm. long and rarely indeed as small as the length 

 given by Smith for piilchella (3J/4 lines = 7 mm.); moreover 

 they have the wings more heavily clouded apically and the basal 

 segment of the abdomen has a yellow band, while vincta has the 

 flagellum heavily dusky in the middle and the scape in front 

 usually strongly suffused with reddish. In the same paper in 

 which he reduced pulchella to synonymy Cresson described 

 Nomada obliterata from a single female from the District of 

 Columbia. In 1897 Robertson described Nomada viburni from 

 two male specimens from Illinois, and in the following year 

 recorded the taking of the female which proved to be conspecific 

 with Cresson's type of A'', obliterata. Since then A'', obliterata 

 has been collected in various localities, and is now known to 

 range from the District of Columbia west through Indiana, 

 Illinois and Nebraska to Montana. A comparison of the de- 

 scription of N. piilchella Smith with a large series of males of 

 obliterata from Nebraska (ninety-six specimens) shows that all 

 of the characters given can be exactly matched in some of the 

 specimens of this series, the only points of variation being that 

 most specimens have the yellow lateral face marks attaining the 

 vertex and the apex reddish. The size varies from 6-9 mm., the 

 wings are faintly clouded on the apical margins, and the basal 

 segment of the abdomen has a transverse ferruginous band, 

 exactly as described for piilchella. The writer feels almost cer- 

 tain that a comparison of the type of A'', pulchella Smith with 

 males of A^. obliterata will show them to be the same species, but 

 until such actual comparison can be made we had best continue 

 to call the species under Cresson's name. 



In Nebraska A^. obliterata flies from April 19 to May 2 and is 

 common at the flowers of Prunus americana and Salix nigra. 

 It has been collected at Lincoln, Cedar Bluffs and West Point. 



61 



