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24.vi this year, from a garden backing onto scrubby shingle and woodland. Clearly a dark basicosta, and (this one I am not 100% sure about) no discal bristles on tergite four (at least nothing as long and strong as the marginals). I've shown some poor images of basicosta, tergite four and genitalia below for comment, but this one will probably have to go to ChrisR at some point.

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basicosta

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tergite four

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side view of genitalis. Unfortunately covered in exudate

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Ewww - as you have a male I would say genitalia are your best best - they are fairly characteristic if you can clean them up a bit. You need both a lateral and a dorsal/ventral view of them and compare them to the figures in our revised key. Also eye- vs. frons-width measurements will help a great deal ... all other features are a bit hard to work out on photos :)

EDIT: C.atricosta is very rare in the UK so if it is looking like that then I'd need to see the specimen myself :)

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I have been using the revised key and the genitalia do seem to show a good match, but it is quite difficult to show with these poor images. Frons width also fits within the range for atricosta. I will send this one on to you Chris

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Ahh, great - I have an atricosta here that I can compare it with ... one that I picked up ages ago and it lay in my collection for ages (misidentified) until we did the revision and it forced me to go over all my material again :D

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was this a yes for atricosta in the end? And as it's a while ago, perhaps a species that has increased recently?

Jeremy

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If you bring it in next time I will have a look at it - as you say, the genitalia look good but I see them so rarely it would be nice to have a look at it :)