Studies of North American Bees ' 39 



Dianthidium (Anthidiellum) robertsoni Cockerell. 



A male from Tucson, Arizona, and a female from the Babo- 

 quivaria mountains, Arizona (both F. H. Snow, coll., 2472) are 

 referable to this southern California species, though presenting a 

 color variety in which the legs are more extensively black, the 

 female having the anterior tibiae yellow at the knees only and the 

 middle tibiae merely with yellow knees and a narrow yellow 

 stripe running two-thirds of the way down the antero-external 

 edge, and the male with the apices of the hind tibiae narrowly 

 reddish (in typical robertsoni the female has the middle tibiae 

 wholly yellow externally and the anterior tibiae with more than 

 the basal half yellow, while the male has both ends of the hind 

 tibiae broadly yellow). The pygidium is wholly black in the 

 female (with two yellow marks in typical robertsoni) . 



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