I was informed this is a Triton, part of the Harbour Monument. From the Wikipedia: Triton (Τρίτων, gen: Τρίτωνος) is a mythological Greek god, the messenger of the sea. He is the son of Poseidon, god of the sea, and Amphitrite, goddess of the sea, whose herald he is. He is usually represented as a merman, having the upper body of a human and the tail of a fish, "sea-hued", according to Ovid "his shoulders barnacled with sea-shells". And: Triton was the father of Pallas and foster parent to the goddess Athena. Pallas was killed by Athena during a fight between the two goddesses. Triton is also sometimes cited as the father of Scylla by Lamia. Triton can sometimes be multiplied into a host of Tritones, daimones of the sea.