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After a few close looks at this fly and the pics of both Halesus in the book I can safely say this looks a bit like a cross between the two.
It has streaks, but I'm not entirely sure they are well enough defined to be radiatus and thats being honest. It actually does look more like digitatus to me after comparing the markings to the close up images in the book. In that example(digitatus) there is a linear dark mark the length of the cell but it is repeatedly joined to the edge of the cell with dark branches.
I cant say for certain, but good clear images of radiatus seem to have very clean edged, well defined streaks within the cells which are not joined up to the periphery of the cell with dark branches.
It'd be good to hear some other opinions on this one of yours. I'm even less sure now than last time, ie I think you might be right in the first place!
Thanks. I have looked at more pics now and think H.radiatus is safe.
Jamie from Briantspuddle
Lat/Lng: 50.7, -2.3
OS grid ref: SY8193