Beat from an oak tree. In the field, I thought this might be Wamba crispulus and excitedly took a couple of photos of this small spider, only to find it had disappeared before I could collect it. Tentatively identified based on the appearance. One more photo and more details here: http://bugguide.net/node/view/1109356

A male was found at the same time and location:
http://bugguide.net/node/view/1110066