and thanks for wanting to be helpful, but did you read our discussion? At this point, I don't think that either Dennis or I are absolutely certain of the ID. I just moved these back to genus because it isn't marginatus , but doesn't seem to be halli either.

I'll check this out - still have the specimen accessible at CSUN.
From northern CA it may seem that Riverside is in the vicinity of the Santa Clara Divide of the San Gabriel Mountains, but its like traveling from Tulare to the Tehachapi Mountains (Of course, this fly could still occur in the San Gabriel Mountains).
I don't know anything about this family, so I'm noting your point about the black squamal rim, and will check back with Jim Hogue.
Haven't had the time yet to carefully look at the specimen, but have obtained a couple of keys [Sabrosky (1948); and Schlinger (1960), which names halli as a new species].
One problem I see, is the length of the proboscis, described by Schlinger as "short, not reaching beyond abdominal segment III, distinctly curved upwards", for smaragdinus "as long or longer than wing length". However, the smaragdinus group, containing the two spp. halli Schlinger, and smaragdinus Gerstaecker], is characterized by having a curved proboscis, and there's more that doesn't seem to fit.
Following the Sabroski key, we're led to marginatus .
Still, I consider this tentative until I can examine the actual specimen, hopefully next week.
Meanwhile, I'd appreciate any comments.

Check out this site for a picture of the type specimen of E. marginatus. http://insects.oeb.harvard.edu/mcz/FMPro?-DB=Species.fm&-lay=web&-Format=search_results.htm&Genus=Eulonchus&-Find

Note the obviously margined squamae behind the wing base.

For some pictures of the type specimen of E. halli you can go to the site you mentioned above at Cal Academy. The curvature of the proboscis is not as prominent as that in E. smaragdinus, but certainly more noticeable than in your pictures or the drawings in the Manual of Nearctic Diptera. Still the length of the proboscis is comparible with the type. I wonder if some curvature comes after drying? I know it becomes more pronounced in E. smaragdinus after the specimens dry. Good Luck!

it'll be interesting to take a look at my specimen + the Diptera tome. I can see that this family is one of your interests, and appreciate your input!
I've seen the type specimen at CalAcademy, but forgot to include the link. For the benefit of others, here it is: Eulonchus halli .
Just visited Aaron Schusteff's images of Eulonchus from the San Emigdios, and read your informative comments.

I pulled out my copy of Cole's 1919 paper on small-headed flies and noted that he has a line drawing of the wing venation of E. marginatus. It matches the types specimen pictured on the Cornell site, but does not match your specimen.

I'm coming to believe that your's and those from the San Emigdio Mountains are extensions of Ev's species in manuscript. I'll post a picture of that species this afternoon. They all would have fallen into the original description of E. tristis, but are not that species. They are blue/purple with dark legs and pale knees, and there is a prominent fringe of pale hairs on the posterior edge of the second abdominal segment. They generally fly in June and are found in the upper chaparral to yellow pine forest. I have specimens from Fresno County south to eastern Kern.

labeled E. marginatus . Six out of eleven were clearly marginatus, and those came from Mt. Hamilton, Sta. Clara County, collected May 28, 1997 (2 females, 4 males), and all on Penstemon heterophyllus flowers.
There were two males, also from Mt. Hamilton, that didn't look like marginatus (no black margin on squamae), though collected on the same Penstemon species. Two others (1 male, 1 female) that didn't fit into marginatus were collected at Agnew Meadow, Madera County, 12 July 1997.
An obvious difference I noticed between the 6 marginatus and the others was the size of the ocellar tubercle - much more protuberant in marginatus , as shown in the type specimen, considerably less so in the others.
I'll try to take some close-up photos, though probably not this week, showing the main characters.
I think for now, to avoid confusion, I should move my photos to genus.

One of the problems with the genus is having so many wide ranging species in the southern half of the state that haven't been described. I have the two from the southern Sierra Nevada that I sat down with Ev and got him to give me the scoop on, but if you use the existing keys you are left scratching various parts of your anatomy wondering what you have. There are a minimum of three undescribed species that I know of, and who knows how many if you start looking in those places of isolated floras and faunas like the desert mountain ranges.

The new species from San Benito County is interesting. Its close to E. timberlakei (in manuscript), but while you have the prominent horn-like ocellar tubercle the ocelli are absent. There are just pale colored areas where the ocelli should be. I have 4 females and 3 males, and hope to get more this comming season. Then I may go ahead and describe it since Ev hasn't got it in his proposed species.

While I have good series on both E. sierraensis and E. timberlakei I can't do anything with them since I know that Ev has them in manuscript.

Did the specimens from Agnew Meadow, Madera County look similar to your specimen? Could they be E. sierraensis?

but I haven't had the time to compare them character by character, was looking mostly for those that were obviously marginatus , and those labeled so, but didn't fit. Also looked at some others, i.e. smaragdinus (yellow legs, curved proboscis longer than abdomen), and sapphirinus (yellow legs, straight proboscis ± length of abdomen).
I'll go over them again, more thoroughly. But first I'll carefully read those three papers & keys. It'll be a good learning experience. If I take some decent photos, I'll post some of them.

One interesting thing about Eulonchus is the presence of sympatric species. You can go to a location one week and get nothing but one species and two weeks later find a completely different fly on the same host. Best floral hosts are Eriodictyon, Diplaucus, Penstemon, Swertia, Monardella, Iris, Chamaebatia, etc. Tubular flowers are the rule. The one exception seems to be E. halli on Cryptantha intermedia.

& tubular flowers make sense considering those long proboscides; Swertia & Chamaebatia would be ok for those with shorter ones.
Thanks also for posting your specimen; the sierraensis does look similar, hope the Schlinger manuscript gets published.

I printed out a copy of the Cole paper this past weekend, and also came up with tristis , but wasn't sure after looking at the type specimen; also wanted to take another look at my specimen, and wait to see what else you might have to say.
I'm really grateful that you took a stab at this ID. By now I'm well convinced that it isn't marginatus , thanks to you pointing to the lack of a black squamal margin.
I'm heading over to CSUN to look at what Jim Hogue has there besides my specimen.
Anyway, you've helped fan my interest in this group of flies, and I'm looking forward to seeing more info. from you, also have put them on my calendar. Luckily we've had some 'drops of hope' (plenty of rays in CA already, its the water we need), so hopefully we'll have a good season ahead.

Hi Hartmut, I posted a couple pictures of the "new" species that Ev has been in the process of describing for the past 20 years (but I'm not bitter ;-) ). I think you'll see the similarities between your specimen and E. sierraensis, but without an official description or both specimens in hand all I can say is they look to be very close.

I'll leave you alone and let you ponder. But first I did get out my copy of Ev's paper on Eulonchus halli (1960), and I find it troubling that you found your's in June and Ev says that halli is clearly a very early emerger that flies in March and April before the other species of Eulonchus come out in June. I need to make the trip this spring to Riverside and track down this species from the type locality for comparison purposes.

That doesn't mean I agree with E. marginatus as the identification, I just don't know.

the squamae, looking at the Harvard images.
Here's a link to CalAcademy images of halli , also showing the much shorter proboscis. This makes sense when considering that this fly has been mostly reported on Cryptantha . Schlinger writes about the short proboscis of halli being "...well adapted to be inserted into the short corolla of C. intermedia ...".
P.S. Just saw your new comments, and thanks for that! I'm learning in the process, will also take a look at the "Manual of Nearctic Diptera" , but will have to wait 'til next week.