Studies of North American Bees 15 



Mandibles bidentate; head and thorax of female red, with the 

 sutures, depressed and concealed portions black; apex of male 



notched Gnathias 



(Type Noinada hella Cresson) 



Vertex and mesoscutum smooth and shining; male entirely black, 



female with head and thorax black and abdomen wholly red ; apex 



of male rounded and entire; mandibles simple; posterior femora 



of male with a tooth beneath at base Melanomada 



(Type Noinada griiideliae Cockerell) 

 Anterior coxae with strong pubescent spines, longer in the female ; abdo- 

 men usually very distinctly punctured. 



Antennae of male peculiar, sharply bicolor at least basally, being 

 yellow below and blackish above, the scape robust, joint 4 

 attached obliquely to and very much longer than 3, usually 

 nearly =5-|-6, 5 distinctly spined above, 6-9 short, distinctly 

 crenulated above, 10-13 heavier and longer, straight, apical joint 

 acutely pointed; antennae of female ordinary but joint 3 shorter 

 than 4. 

 Female red, with sutures, depressed and concealed portions black, 

 the abdomen finely but usually quite distinctly punctured, the 

 margins of the segments not reflexed ; antennae of male with a 

 pale annulus, and the apex of the male strongly notched. 



Nomad Ilia 



(Type Nomada arficulata Smith) 



Female black, with red and yellow ornaments, the whole body 



strongly and coarsely punctured, the abdomen with the margins 



of the tergites cor 'cuously reflexed ; antennae of male without 



a pale annulus, ai.d the apex of the male slightly notched. 



Centrias 



(Type Nomada erigeronis Robertson) 



Antennae of both sexes ordinary, joint 3 exceeding 4, that of the male 



not sharply bicolor, the scape slender, the flagellum not spined 



nor crenulated nor the apical joint acutely pointed; black, with 



yellow and red ornaments; strongly punctured; apex of the 



male usually bifid Micronomada 



(Type Nomada modcsta vegana Cockerell) 



Subgenus Nomada Scopoli, 1770. 



KEY TO THE NEBRASKA SPECIES 



Females 



Joint 3 of antennae about one and one-third times as long as 4; propo- 

 deum with the sides red and covered with a peculiar appressed 



15 



