Obtained from a coin dealer in the 1980's, this is a very nice example of the sea turtle staters from the 500s BC.  I guarantee it's authenticity.

Obverse: The first coins produced on the island of Aegea were minted around 600 BC. The coins feature a sea turtle on the obverse, which represents the island's naval strength and resiliency. Aegea is a rocky and mountainous island in the Saronic Gulf located about 25 miles southeast of Athens. Because of its limited availability of cultivable land, the inhabitants needed to leverage the sea for their livelihood. They became expert merchants and tradesmen, dominating the shipping industry early in the sixth century BC.  The turtle feature has been quite worn down over the millenia, but you can still make out the sea turtle with flippers at the sides and a small 4-prong banker's mark on the middle of the shell.

Reverse: The Aegean turtle bore a close likeness to that of its live counterpart, with a series of dots running down the center of its shell. The reverse of the coin bore the imprint of the punch used to force the face of the coin into the obverse turtle die. Originally this consisted of an eight-pronged punch that produced a pattern of eight triangles. Later, other variations on this were tried. In 480 BC, the coin received its first major redesign. Two extra pellets were added to the shell near the head of the turtle, a design not seen in nature. Also, the reverse punch mark was given a lopsided design.

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Era: Ancient Greek

Location: Islands off Attica, Aegea

Date: Circa 500 BC 

Denomination: AR Stater 

Obverse: Sea turtle, head in profile, with banker's punch mark on shell

Reverse: Incuse square with 'proto-skew' design