Bembidion femoratum

This came to ligth in my garden. I really struggled to put a name to it, arriving at Bembidion genei each time I tried to key it. However, whilst that is superficially similar, there were a few things that seemed to be not quite right, including the pattern of the elytra and the shape of the pronotum. It surely wasn't genei, but I could not figure out where I had gone wrong keying it. I tried dissecting it to see if the genitalia could give me a clue, but it turned out to be a female. Eventually I gave up and put the beetle to one side to come back to at a later date. This I did a year or so later, and again my first attempt keying it using Duff got me to genei. Still I could not see where I had gone wrong, but this time AI did a better job of pointing me in the right direction, being 100% sure it was femoratum. An initial image search for that species was encouraging, but I needed to get to this using the keys. It turns out that either I should have interpreted the pale patches at the base of the sides of the elyta as not being "definite pale humeral spots" or the median base of the elytra as being pale. I'm honestly not sure which one of these options is where I went wrong - it doesn't seem unreasonable to interpret the pale patches as definite spots to me, albeit bigger spots than some other species that key that way, and the central part of the base of the elytra (taking this to mean both elytra together) is clearly dark. Maybe it means the median base of each elytron, in which case the pale patches probably did just about extend over this, but if that's what it means it isn't clear from the way it's worded.

Even after getting it to the right subgenus, keying it wasn't totally easy. I really struggled to see the fine punctures just in from the back of the eye. I had to hold it at just the right angle with good lighting to see these.

Bembidion quadrimaculatum showing head (2 angles plus a close-up of the punctures in from the eye), base of antenna, pronotum, base of pronotum, elytra, discal puncture of elytron and spermatheca, North Elmham (Norfolk, UK), 18th July 2024

At 4.6mm this beetle was much larger than a Bembidion quadrimaculatum that appeared in the same trap.

Bembidion quadrimaculatum (left) and Bembidion femoratum (right), North Elmham (Norfolk, UK), 18th July 2024