This is a Barbados On His Majesty's Service Cover from 1893.  It was sent locally in Barbados on 2/24/1893.

One thing to note with this one is that it was sent during a shortage of the Barbados 1/2d Postage stamp.  As such, the BLACK CROWN CIRCLE BARBADOS Marking was used in lieu of postage stamps.  There is a CDS dated 2/24/1893, along with a BLACK OVAL CROWN CANCEL.  There is a trace of another CDS on the back, but it is unreadable.