Omalium rivulare

Keying this to genus was easy enough but getting it to species was a little trickier. The size helped rule out several of the smaller species although Hackston doesn't provide a size for Omalium excavatum which was one of the more challenging ones to eliminate. The abdominal microsculpture was hard to see well enough and the pronotum shape difficult to judge, but I think I was right to elimate excavatum - although not explicit in the key photos of that species show dark first segment of the antenna.

I had left this beetle on a windowsill for quite some time so it was very faded when I examined the specimen so don't take any notice of the colour of the head shot below. It was intended to show the rounded impressions in front of the ocelli and the rounded temples, not the colour.

Omalium rivulare with close-up of (faded) head, North Elmham Cathedral Meadows (Norfolk, UK), 30th April 2019