(n.) Also Hippocampos or Hippocamp.
The hippocampus is a mythical creature of ancient Eurasian cultures depicted as being part horse and part fish or dolphin, featured on coins as ancient as the gold 50 asses of Etruria (211 BCE-200 BCE) and as modern as the U.S. 1915-S Panama Pacific International Exposition commemorative $2.50 gold quarter eagle. The hippocampus on the Pan-Pac coin is surmounted by the personification of Columbia holding a caduceus in her left hand.
The hippocampus is used in heraldry as a heraldic charge, in much the same way as a lion, griffin, or eagle (etc.) might be.
The term is also used to describe the seahorse (Hippocampus hippocampus) and the portion of one’s brain responsible for storing memories and conveying emotion.
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Ironically, I was just looking at a nice example being offered on Great Collections! I’m unfortunately not in the market, however this is a really cool coin IMO. Like many others here, I’m sure, I am quite fond of the Pan Pacific offerings in all formats(sizes), denominations, medals, as well as metals. The octagonal $50 is one of, if not, my all time favorite design. Thanks for the tidbits on the use of hippocampus in the design!