Official stamps. 1894, Hippopotamus, red overprint ''O S'' on $1 ultra and black, complete sheet of ten (2x5), full OG, NH (middle stamps) or hinged, VF, C.v. $275 as hinged singles (Image)

Official stamps. 1894, Hippopotamus, red overprint in capital letters ''O S'' on $1 ultra and black, this overprint in green or black had been used for $2 and $5 stamps only, full OG, LH, VF and scarce, L. Miro expert’s hs on reverse (Image)