Reverse: z:hISPANIE:z:ET:INDIARV:M:. (reverse-barred N in hISPANIE and INDIARV . (M is Roman, replacement letter; z is a squarish emblem punch, possibly an "alef") - Crowned Pillars of Hercules; PLVS between, in overlapping rhomboid panel slanted left; 4 above.
Assayer mark believed possibly to be P/R (R is makeshift, recut letter). Nesmith 6d/-- (unlisted rev. die); rev. similar to that of Nesmith 6d, but no rondule in corners of rhomboid PLVS motto panel; on the possibility that the initial mark "z" may in fact represent the Hebrew letter alef, suggesting a Jewish mint worker, see David L. Nathan, "A Hebrew Letter on the New World's first Coins?" in Shekel, v. 39, no.1, jan.-Feb. 2006, p. 8-15