Anthobium unicolor

This was collected from a pitfall trap (in propylene glycol, so no live photos) and I had a couple of challenges keying it out. Firstly I couldn't make out the impression just in front of the ocelli when I was looking at it wet. I subsequently discovered that these were easier to see when the beetle was out of the liquid (though still not very easy), but my initial inability to see them delayed me getting to the right genus. Then I wasn't convinced which Anthobium it was - the head was clearly much darker than the pronotum so I was expecting it to be atrocephalum. Possibly supporting that, the elytra were clearly longer than their combined width and 2.5 x longer than the pronotum - in other words proportionately a little longer than Hackston suggests they should be for unicolor. But the shape of the pronotum (clearly concave before the hind corners) and the elytra broadening back from the shoulders suggested unicolor. The elytral puncturing fitted the description for unicolor better too, and the relatively large size was another character in favour of unicolor. Of all these the pronotum shape was the most unequivocal and, I judged, the least likely to show variation, so I figured it was probably unicolor. Fortunately it was a male and that meant I could remove any doubt by examining the genitalia, and this (along with the mid tibia shape) clinched it as unicolor.

male Anthobium unicolor showing head & pronotum, close-up of head, elytra and aedeagus (2 views), Wendling Beck Environment Project (Norfolk, UK), 29th to 31st March 2024