...I think the reason that I included it was that not having seen many of these I found that diamond shape on the thorax sort of unusual. Probably it is not that unique and I will frass it.

is an artifact of lighting, combining the scutellum (here dark) with the posterior part of the scutum (probably with yellowish scales).
This seems to be a widely distributed Villa ; compare with Tom Murray's photo 1 .
Your far right image is useful in that it clearly shows wing venation, including vein R2+3 (note that it comes off the third longitudinal vein at a right angle, typical in Villini).
You may be interested in playing around with CSIRO's Anatomical Atlas of Flies , an excellent resource for general fly anatomy.

Thanks, Hartmut, and I did realize that the apparent marking was not a mark per se, and I was just using my description to give a general idea of the location of the feature I was talking about.

I have been lamenting my lack of good anatomical resource material. I am going straight to the page you linked to, though, because it is really making life difficult not having the right terminology at my disposal. I am deeply indebted to you for your assistance!

Thanks for the info. As appealing as it sounds I think I'll pass on the dissection of genitalia:0