Unknown Bat ID-Costa Rica (1 Viewer)

I was surprised and pleased to see that BirdForum has a Bats forum. I am wondering if anyone can ID (or thinks it is possible to ID) the bat species within this photo. It was taken in January of 2010 near the base of the volcano Arenal in Costa Rica and has been cropped. In trying to research online, it looks like the book I want to find is Mamíferos del Area de Conservación Arenal, but I am unable to find a copy that is easily accessible. Does anyone have any thoughts or pointers?

Thanks.

Gives the impression of Tent-making Bats, but really hard to discern any useful features that could clinch an id.

James