Set of Three Carved Stone (Game?) Blocks

This is a set of three carved volcanic tuff stone blocks with incised decoration. The largest (a) is a flat, squared off piece with incised round markings probably made by twisting a hollow cane in place to the desired depth, arranged in rows within an x-shape defined by incised lines. The markings are on the diagonal from each of the four corners to its opposite, crossing in the center. The two smaller pieces (b and c) are rectangular, with rows of three round markings on each of the four long sides, pierced lengthwise with holes which run completely through each piece.Many similar blocks have been found on the Isla de La Plata, Ecuador, with a few from the neighboring islet of Cayo. None have yet been recovered from the mainland. Although most are decorated much as are these in the Johnson Museum collection, some plain, unmarked ones have been found, and the number of circles on each block varies. The true nature of these stones is problematical; it has been proposed that they may be part of some kind of game, or that they are some kind of navigational device or fishing net weights.