192 ERNEST A. BACK. 



me to believe that this is a character as little to be relied upon 

 as those of the antennas 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 con sanguineus, 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 7. 



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. 



breviusculus. 



Pile and bristles of thoracic dorsum, especially along the middle 



line, black 4 . 



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



Not as above 5 . 



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



in extent gratus. 



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



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



albibasis, nigritus. 

 Length over 16 mm.; third segment of antennas elongate. 



inquinatus, morosus, modestus. 



7. Third segment of antenna; elongate, style short, thick, sometimes 



longer and more slender; first posterior cell more frequently 



open : 8. 



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

 terior cell more frequently closed 12. 



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

 never seen. 



