Watch List notes:

MEGARIS. Megara. Circa 375-338 BC. Trihemiobol (Silver, 12 mm, 1.50 g, 9 h). Laureate head of Apollo to left, his long hair falling down the back of his neck. Rev. Μ - Ε - Γ Triskeles of crescents curving to right. BCD Peloponnesos 5. BMC 3 (no denomination). SNG Copenhagen 462 (Attic triobol?). Traité II, 3, 106 and pl. CXCIV, 9 (Corinthian triobol). Very rare. Well-centered, attractive and unusually nice. Porous surfaces, otherwise, good very fine.
From the "Collection sans Pareille" of Ancient Greek Fractions, ex Peus 368, 25 April 2001, 145.

This is certainly an Aeginetic trihemiobol (putative weight, 1.55 g) rather than any of the other strange denominations it has been termed: various triobols, for example. It was also struck in very small numbers and, like all the other coins of this series, it is commonly found in rather worn condition (if found at all). The fact that these coins usually appear in a worn state indicates that they circulated for a considerable time and were not hoarded when new; it also suggests that Megara simply was not prosperous enough to require a larger coinage. Thus, despite this coin's rather pitted surfaces, it is remarkably fine example of this elusive coinage!