Mark Sturtevant wrote:
So the weird little spiders that steal out of other spider webs are in the genus Rhomphaea, and we have 2 species. You know these spiders, of course. But this one is not quite a match to either species, so right now I don't know what it is.
I agree.
The second photo, enlarged, shows the spinnerets clearly on the odd shaped abdomen.
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There are a couple of shots on this link that look real close.