Watch List notes:

ISLANDS OFF ATTICA, Aegina. Circa 525/0-500 BC. Obol (Silver, 9 mm, 0.96 g). Sea turtle with a T-shaped design formed a horizontal line, or "collar", and three very large pellets down the back of its shell. Rev. Quadripartite incuse square in a mill-sail pattern. Meadows, Persian, Aegina Group IIb. Milbank pl. I, 8. Rare. Very attractively toned and boldly struck. About extremely fine.
From the "Collection sans Pareille" of Ancient Greek Fractions, and from the collection of L. Mildenberg, ex Münzen und Medaillen FPL 373, November/December 1975, 58.