These are my favorite set of dominoes I've ever found, and I've found a bunch! My guess is these--with no wooden backs, just bone--were sailor made, 19th century for sure, and one can just feel whoever that maker was carving out each piece and then every single dot. Both the shapes and the placement of those dots is wonderfully irregular, as is the bone itself, adding up to just about the most purely beautiful set of dominoes as I can imagine. And on a few of the backs were carved letters and marks; I clearly see an "A" and also what looks like "NW."
Complete double six set of 28. These are small in size--each piece measures approx. 1 1/4" x 9/16" x 3/16. I am not sure if the slide-top box I found them in was made custom for them, but it too is quite old and they have clearly been held in it for a very long time. It measures 4 1/4" x 1 7/8" w x 1 1/4" t. All in very good antique condition, with a very minor chip here or there.