258 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Sek. 



species through the key. Under "31" is an alternative, re- 

 ferring to the length of the distal segment of the fifth vein, that 

 may cause some confusion. I could find no satisfactory char- 

 acter to take the place of this, but in case of doubt, the follow- 

 ing note may be of assistance. Of the four species that run 

 through "31" to "32-34" veles Lx)ew can be separated by its 

 third and fourth veins being more widely divergent at their 

 tips than in the other species, and in fact, than in most of the 

 species of this genus; modestus V. D. has the halteres infus- 

 cated and the feet black; calif orniensis Wh. has the second 

 joint of the hind tarsi fully twice as long as the first, while in 

 distinctus, new species, it is only one and a fourth times as 

 long as the first. 



I have described several species from females, as it seems 

 to me that in this genus the females are as a rule as easily 

 separated as are the males, there being few secondary sexual 

 characters in the males. 



This paper is not a revision of our species but only intended 

 as a help to those w'ho, like myself, have tried to determine 

 their material and have found most of their species unde- 

 scribed. I hope someone with more material and better 

 equipped for the work will make a thorough revision of our 

 species. 



Table of North American Species 



1. Scutellum with one pair of bristles (there may be a pair of small 



hairs outside of these) 2 



-. Scutellum with two pair of bristles (the outer ones may be small) . 11 



2. Antennae, proboscis and legs, including fore coxse, yellow 



novus, new species 



-. Amtennse, proboscis and more or less of the femora black 3 



3. Thorax with distinct vittse 4 



-. Thorax without distinct vittae 10 



4. Thorax with a median bluish green vitta obesus, new species 



-. Thorax with a median brown stripe running its entire length 5 



5. Wings with a brown cloud ait base of third vein 6 



-. Wings without a distinct cloud at base of third vein 7 



6. Tibiae and tarsi yellow cuneiformis, new species 



-. Tibiae brownish; tarsi black with the base of metatarsi yellowish.. 



(female of) nitidiventris, new species 



7. Abdomen bluish but with gray pollen ; male with the front pro- 



duced into a four-sided pyramid petulcus Wh. 



-. Abdomen shining black, front normal 8 



8. Tibiae and tarsi mostly yellow similis, new species 



-. Tibiae and tarsi black or brown 9 



