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I saw this at Yucab, Cozumel, April 8, 2012 at about 30 feet.  The closest thing I could find in DeLoach's book is Lesser Electric Ray, but they aren't supposed to be in Western Carribean?  at least accdg to DeLoach's book.  (Cozumel doesn't appear to be in Southern Caribbean).   But an Audubon book does say Yucatan so that would encompass Cozumel.  Hope you can clear this up for me!

Thanks for your help!