A. ‘"Floridian"’ at Castle Pinckney.
--Among the prisoners at Castle Pinckney is one Peter Foster, who has been a pilot at Fernandina for many years past. Some weeks ago he managed to find his way to the blockading fleet, and thence to Boston. He subsequently volunteered in one of the Massachusetts regiments, fought against us at the battle of Manassas Plains, was taken prisoner and carried to Richmond, whence he was recently transferred to Castle Pinckney.