Watch List notes:

WEIGHTS, Macedonia or Thrace. Uncertain city. Circa 370-340 BC. Weight of a Hemitriton or 1/6 Stater (Bronze, 35x35x20 mm, 133.00 g), a commercial weight on the Attic standard, with possible traces of an illegible inscription on the edges. Tortoise seen from above. Rev. Plain. For an Athenian bronze weight with a turtle see Agora X, p.26 and pl. 1, BW3 ( dated to c. 500 BC); for Athenian lead weights with tortoises, very similar to this piece, see Agora X, pp. 29-30, and pl.7, especially LW 34 (dated to the 2nd quarter of the 4th century BC or later into the 3rd century). A fascinating probably late Classical weight related to similar examples from Athens, but almost certainly not from there. Rough surfaces with a green-black patina. Good very fine.
From the collection of the late T. Skoupidiopoulos, formed in the 1970s and 1980s, and said to have been found in Thrace.

It should be clear that this is a tortoise, rather than a turtle, because of its round, albeit rather squarish shape: sea turtles are more oval in appearance, and with a slightly pointed tail end. It's date has been established through its strong resemblance to the datable pieces from the Agora; the possibility that it might be of mid 5th century date, after the change from turtles to tortoises on the coinage of Aegina, is not all that convincing given the abundance of later parallels.