Studies of North American Bees 7 



with long black bristles, becoming copious laterally on tergites 3-6. Py- 

 gidium coarsely punctured above, the dorsal valve terminally broadly 

 rounded, the ventral valve much surpassing the dorsal valve and produced 

 into a long, oval lobe on each side. Venter subopaque, minutely punctured. 



Type. — Moscow Mountain, Idaho, $. 



This species is a typical Chelynia and belongs to the nitida 

 group. It is closest to w?. (Chelynia) subemarginata Cresson, but 

 differs at once in the deeply bilobed ventral valve of the pygidium 

 (in subemarginata the ventral valve only slightly exceeds the 

 dorsal valve, and is broadly truncate with the sides scarcely 

 produced into lobes), and in having the second submarginal cell 

 only, about one-fourth longer than the first ( fully one-third longer 

 in subemarginata) ; from S. (Chelynia) nitida Cresson it differs 

 in its close and rather coarse puncturation (nitida is sparsely and 

 finely punctured), and in having the bands on tergites 1-4 broadly 

 emarginate laterally on the posterior margin ; while from S. 

 (Chelynia) monticola Cresson it differs again in the close punc- 

 turation and also in the oblong ovate abdomen (the abdomen is 

 short and subglobose in monticola) . The pygidium is very dif- 

 ferent from that of 5". (Chelynia) rubi Ckll. From^. (Chelynia) 

 elegans Cresson, subcaerulea Cresson, and pulchra Crawford it 

 differs in its wholly black ground color, without a trace of blue 

 or green, and in the bilobed ventral valve of the pygidium ; from 

 S. (Chelynia) pavonina Ckll., cusackae Ckll., and calliphorina 

 Ckll., in its black color and in the possession of creamy bands on 

 tergites 1-5 ; from 5". (Microstelis) montana Cresson, senecio- 

 phila Ckll., and carnifex Ckll., in the black color and in the 

 different venation. From 5". (Microstelis) obesa Say, costalis 

 Cresson, rudbcckiariim Ckll., louisae Ckll., and laticincta Cresson, 

 and from 5". (Stelidiiim) trypetinum Robertson, it may be dis- 

 tinguished at a glance by the complete lack of yellow ornaments 

 on the head and thorax, while the red ornaments of 5. australis 

 Cresson serve to easily distinguish that species. By its much 

 larger size it may be easily separated from the other North Ameri- 

 can species of the genus, viz., foederalis Smith, birkmanni Ckll., 

 lateralis Cresson, permaculata Ckll., sexmaculata Ashmead and 

 interrupta Cresson. 



