(Seahorse Mailbox) in Treasure Island, Pinellas County, FL. 107th Av. (becomes Treasure Island Causeway) E. 0.4 miles from jct with FL699 (Gulf Blvd) to the mailbox on the S. side of the road at 1. (N27 46.237 W82 45.761) Photo by Jack & June Schmidt 6-6-10.