192 ERNEST A. BACK. 



me to believe that this is a character as Httle to be rehed upon 

 as those of the antennae and wings, for from the perfectly- 

 bare hypopleura of breviusculus, jubatus, nigritulus, etc., can be 

 found gradations from a hypopleura with a very slight amount 

 of pile to one with well-developed bristles such as that of 

 picticornis. It is significant that a number of species, such 

 as longulus and consanguineus , good Stenopogons in other 

 respects, have a small amount of pile on the hypopleurae. 

 Consequently, having failed to find any character or set of 

 characters, by which the genera can be satisfactorily separated, 

 I have made Scleropogon a synonym of Stenopogon. I am 

 confident, however, that generic subdivisions can well be made 

 when carefully collected material is brought together. 



This genus is abundantly represented in our western plains 

 and in California. 



SYNOPSIS OF SPECIES.* 



1 . Hypopleura bare 2 . 



Hypopleura with hair or bristles "f. 



2. Sternopleura with a tuft of long fine pile 3. 



Sternopleura without such a tuft, though usually with some pile. ...6. 



3. Pile and bristles of thoracic dorsum wholly dull yellowish, the 



posterior portion of the dorsum unusually bristly. 



brevisciiluf^. 



Pile and bristles of thoracic dorsum, especially along the middle 



line, black 4 . 



4. Black; wings black, white at base jnbatus. 



N o t as above 5 . 



5. Abdomen above with a reddish-yellow vitta, sometimes variable 



in extent g'ratlis. 



Abdomen without such a vitta.. ..californiae, obscuriveiitris. 

 tj. Length 10-13 mm.; third segment of antennae more oval. 



albibasis, iiigritiis. 

 Length over 16 mm.; third segment of antenna? elongate. 



iiiqiiinatiis, inorosus, iiiodestiis. 



7. Third segment of antennae elongate, style short, thick, sometimes 



longer and more slender; first posterior cell more frequently 



open 8. 



Third segment of antennas more oval, style bristle-like; first pos- 

 terior cell more frequently closed 12. 



* This key does not include ochraceus or shnilis, which I have 

 never seen. 



