134 Proceedings of the Biological Society of Washington. 



3. Face clothed with light colored pile 4 



Face clothed with black pile modestus n. sp. 



4. Abdomen wholly black beyond the second segment; antenna? 



slender bombiformis Tnsd. 



Abdomen with patches or bands of light colored pile beyond second 

 segment; antennae much shorter, the third joint much thick- 

 ened and tapered to a blunt point coloradensis Ckll. & Andr. 



5. Second abdominal segment dorsally with broad impressions at 



sides on anterior half, the lateral margin convex . rtificrus Will. 

 Second abdominal segment simple 6 



6. Antenna? unusually long and slender, the third joint as long as 



the first, subcylindrical, nearly uniform throughout, the tip 



bluntly rounded tristis Loew 



Antenna? normal, the third joint more or less thickened toward 

 the middle 7 



7. Pile on frons mostly black ; body deep blue piperi n. sp. 



Pile on frons wholly pale 8 



8. Body color blackish cothumatus Big. , eastern form. 



Body with cupreous or bluish reflections . cothumatus, western form. 



Microdot! cothumatus Bigot. 



This is the species that has been treated by Williston and subsequent 

 authors as tristis. In eastern specimens the general body color is black 

 and without metallic coloration. The pile on the head is pale through- 

 out. The antennae are rather stout, the third joint subequal with the 

 first or a trifle shorter. The third joint is thickened and compressed, 

 thickest a short distance beyond base; when viewed in its broader aspect, 

 it is broadly rounded at the tip. The scutellum is convex and shows 

 hardly any trace of emargination, while the teeth are minute. In darkly 

 colored specimens the legs are piceous, with but slightly lighter brownish 

 shades at the bases of the femora and narrowly on the knees ; the whitish 

 pile is densest on the tibiae and the hind tarsals have a cushion of dense 

 short yellow hair ventrally. In poorly or incompletely pigmented speci- 

 mens the legs are more or less ferruginous or yellowish brown, the tibia? 

 often lighter colored than the femora. In the male the hypopygium is 

 more or less fully tinged with ferruginous. In the less deeply pigmented 

 specimens of both sexes the same shade extends along the sides of the 

 abdomen, as well as along the apical margins of the segments. The 

 specimens before me that answer to the above description are from east 

 of the Rockies. The localities represented are as follows : 



New York, Connecticut (Williston collection); Springfield, Massachu- 

 setts (G. Dimmock); Mount Tom, Mass. (Knab) ; West Point, Nebraska 

 (U. S. Bur. Ent. no. \\\f>%, reared from larva? collected by L. Bruner); 

 Eagle Harbor, Michigan (H. G. Hubbard). 



Specimens from the Rocky Mountain region differ from the eastern 

 ones in the dark coppery or metallic greenish blue color of themesonotum 

 and the bluish tinge of the abdomen, but agree in all other respects. 



