Εχιδνα
A monster with the torso of a woman and a serpent's tail instead of human legs. Accounts of her origin differ: according to Hesiod she was the the daughter of Phorcys and Ceto; other versions claim that she was descended from Tartarus and Gaia, or from Styx, or from Chrysaor (Table 12 and Table 32). Echidna inhabited a cave either in Sicily or in the Peloponnese. She used to devour passers-by until eventually she was killed by Argos. Many monstrous offspring were attributed to her: by Typhon she is said to have given birth to Orthrus, the dog of Geryon; to Cerberus, the guardian of the Underworld; the Lernean Hydra; and the Chimaera. Orthrus allegedly fathered Phix, a Boeotian monster, and the Nemean Lion. The dragons guarding the Golden Fleece and the Garden of the Hesperides are said to have been Echidna's offspring, as was the eagle of Prometheus.
Those who lived in the Greek colonies on the Euxine Sea, used to recount a quite different legend concerning Echidna. According to this version, when Heracles visited Scythis he left his horses to graze while he slept and when he awoke he found they had disappeared. As he searched he came across Echidna in a cave; she promised to return his horses if he agreed to couple with her. He consented, and as a result Echidna gave birth to Agathyrsus, Gelonus and Scythes.
{E2 DICTIONARY OF CLASSICAL MYTHOLOGY}