Studies of NortJi American Bees 13 



Micronomada, and undoubtedly the former should be considered 

 a synonym of the latter. 



Centrias and Xoinadida are chiefly characterized by the spined 

 coxae and the peculiar antennae of the male, in which latter 

 character they differ from Micronomada, which has also a dif- 

 ferent proportion of the antcnnal joints which seems to hold 

 good. The differences of puncturation, color, reflexion of the 

 abdominal tergites on the apical margin or lack of it, etc., would 

 seem to justify the continued recognition of these two groups as 

 subgenera. 



Family XOMADIDAE 



KEY TO THE NEBRASKA GENERA 



Maxillary palpi 6-jointed; marginal cell pointed at the apex and not 

 separated from the costa, the second submarginal cell receiving the first 

 recurrent nervure well before its end; color not entirely black but with 

 yellow or red tegumentary ornaments except in males of the subgenus 

 Melanomada; pygidium broadly rounded in both sexes, in the male with 

 the tip sometimes notched or bifid; mandibles simple except in the sub- 

 genus Gnathias; legs ordinary in both sexes ; inner orbits of male sub- 

 parallel, the face broad Xomada 



Maxillary palpi 5-jointed; marginal cell blunt at the apex and remote from 

 the costa, the second submarginal cell receiving the first recurrent 

 nervure very near its end; color entirely black except for brownish 

 stains on the legs in the male; pygidium in the female elongate acumi- 

 nate, and in the male elongate spatulate with the base constricted ; 

 mandibles deeply bidentate ; legs very heavy, the last four femora of 

 the male incrassate; inner orbits of male strongly converging above so 

 that the lateral ocelli are distant from the eyes less than their own 

 diameter, the face narrow Viereckclla 



Genus Nomada .Scopoli, 1770 



KEY TO THE NEBRASKA SUBGENERA 



Anterior coxae simple, rarely with short, indistinct spines (Nomada spp.) 

 or tiny tubercles (Heminoiiiada spp.) ; abdomen usually very mi- 

 nutely or not distinctly punctured. 

 Vertex and mesoscutum more or less roughened by punctures ; male 

 never entirely black nor female black with a red abdomen. 

 Mandibles simple. 



Apex of male bifid or notched, or at least terminally truncate 

 with a slight median emargination ; antennal joint 3 of 



13 



