Capt. Semmes.
--The Nassau Guardies, of the 17th, states that Captain Semmes, of the Alabama, arrived at St. Thomas on the 25th ult., landed at the back of the Island, crossed with three of his officers, and went directly on board a sixteen gun ship — the Georgia — and put out to sea before daylight, while Admiral Wilkes, with the federal craisers, was watching his movements.