Thelxion
In conjunction with Telchin, murdered Apis, when he attempted to subjugate Peloponnesus; but they themselves were slain in return by Argus Panoptes. (Apollodorus etc.) Pausanias (ii. 5. § 5) calls him a son of Apis and the father of Aegyrus.
From Smith's Dictionary of Greek and Roman Biography and MythologyFrom Apollodorus II
He and Melia, daughter of Ocean, had sons, Phoroneus and Aegialeus. Aegialeus having died childless, the whole country was called Aegialia; and Phoroneus, reigning over the whole land afterwards named Peloponnese, begat Apis and Niobe by a nymph Teledice. Apis converted his power into a tyranny and named the Peloponnese after himself Apia but being a stern tyrant he was conspired against and slain by Thelxion and Telchis.
From Description of Greece by Pausanias Book 2
[2.5.7] This Apis reached such a height of power before Pelops came to Olympia that all the territory south of the Isthmus was called after him Apia. Apis begat Thelxion, Thelxion Aegyrus, the Thurimachus, and Thurimachus Leucippus. Leucippus had no male issue, only a daughter Calchinia. There is a story that this Calchinia mated with Poseidon; her child was reared by Leucippus, who at his death handed over to him the kingdom. His name was Peratus.
