Tasgius ater (?)

I found this pair of copulating beetles on a tree trunk with a third, which I assumed to be the same species, nearby - if I remember rightly it was at the base of the same tree. I retained one - my notes suggest it was one of the pair that I retained but the way I labelled the photos suggests it was the third individual.

At the time I did not have access to a key to Tasgius and Ocytus (I had got it that far using Mike Hackston's keys) but after some correspondence with Mike he provided a key to the two genera, though I can't find that on his new website (but I can now find the German key which I think might be the one he used as a basis). Using his key I identified my specimen as Tasgius ater, though I noted in my correspondence that I had struggled to be sure if I was seeing two sizes of pronotum puncture - there was variation in size but this seemed to be more clinal than two clear size classses. Also, although some punctures were clearly separated from one another by more than the diameter of the puncture, this didn’t seem to be the case across the entire pronotum. My mind was made up by a comment that ater was the only member of the genus having epimera of the pronotum and this, I thought, had epimera.

I didn't retain a specimen and my photos are not clear enough to see the detail I saw under the microscope at the time, and I have to say that looking back I wonder if I might possibly have made an error. Perhaps not, but there are photos of Tasgius ater online that show larger more spaced punctures on the pronotum than are evident in my photos. On the other hand there are other photos at least purporting to show Tasgius ater where the pronotum looks extremely similar to how it does in my photos. As for the epimera, I wonder if I correctly understood exactly what that meant at the time, because I'm not sure I do now! I would like another chance to compare another ater with one of the other Tasgius.

If I misunderstood the puncture details and the epimera then judging from Lott & Anderson I think the identification falls between melanarius, globulifer and winkleri, with I think the latter two matching the pronotum shape best.

I think for now I must consider this record unproven, though maybe when I have more experience of ater I will be able to review this and be more confident (one way or the other).

2-3x possible Tasgius ater North Elmham Cathedral Meadows (Norfolk, UK), 2nd December 2018