I think I'm right in putting this pair in Cetema, beyond that I need help. As I understand it the Fennoscandia Frit-flies volume lists four species, three of which have long hairs on the anterior and mid tibiae of the male. I don't see those here which would suggest C. elongata. However, the UK checklist has 6 species in the genera and I don't know whether there is a publicly available key to the genus in the UK.
(Photo only, 11.vii.2020, marshy fields, VC55. Hopefully I'll be able to get a a specimen this year.)
Any help or comments appreciated.
John and Barbara Ismay have produced a key to males, but looking at it, it seems to rely on characters which are not readily visible in your photo.
Thanks Tony, looks like I will need to try and get a specimen then.
Is that key available online? I have tried to contact John and Barbara a couple of times via the Chloropid Study Group page (https://www.dipterists.org.uk/chloropid-group/home) but got no response. I'm not sure whether everything is properly set up yet.