Studies of North American Bees 9 



vertex and mesoscutellum and in the wholly black color of the 

 male, as well as possessing good palpal characters. It has even 

 been suggested that this group may be worthy of recognition as 

 a perfectly distinct genus (Cockerell, Proceedings U. S. National 

 Museum, XXXIX, p. 649), and further study may demonstrate 

 that this is advisable. In some ways it resembles the genus 

 ViereckeUa, but Melanoiiiada has the maxillary palpi 6-jointed, 

 with the apical joint long, the apical abdominal segment broadly 

 rounded in both sexes, the marginal cell pointed at apex and not 

 separated from the costa, the mandibles simple, the legs normal, 

 etc., while ViereckeUa has the maxillary palpi s-jointed with the 

 apical joint extremely minute, the apical abdominal segment 

 elongate acuminate in the female and elongate spatulate in the 

 male, the marginal cell blunt at apex and remote from the costa, 

 the mandibles deeply bidentate and the hind femora of the male 

 incrassate. 



The subgenus Heminomada, elevated to the rank of a genus by 

 Robertson, is simply a Xanthidium in which the first transverse 

 cubital nervure and sometimes the second also is wanting or 

 aborted in one or both wings in about three-fourths of the ordi- 

 nary run of specimens. The wings are not, as stated by Cockerell 

 in his original description of the subgenus, always two-celled. In 

 a series of one hundred and one Nebraska specimens of Nomada 

 oblitcrata Cresson, the type species of Heminomada, before the 

 writer, one has the right wing i -celled and the left wing 2-celled, 

 one has the right wing 2-celled and the left wing i-celled, sixty- 

 seven have both wings 2-celled, nine have the right wing 2-celled 

 and the left wing 3-celled, ten have the right wing 3-celled and 

 the left wing 2-celled, and thirteen (13 per cent.) have both wings 

 3-celled. In Illinois Robertson finds 25 per cent, of his specimens 

 with both wings 3-celled. Obviously this venation character is 

 useless to designate a genus or even a subgenus, since one out of 

 every five specimens collected would invariably fall in another 

 group. If we recognize Heminomada we must also provide 

 another genus for the recently described Nomada victrix Ckll., 

 which has the second transverse cubital nervure lacking in both 

 wings of the typical series of three females. All of this is highly 



9 



