Perseis (sometimes called merely Perse) was an Okeanid and one of the many lovers of Helios (who was thusly her cousin). From their unions were born Kirke and Aeëtes and Pasiphae.
Okeanis & Tethys
"And Perseis, the daughter of Ocean, bare to unwearying Helios Circe and Aeetes the king. And Aeetes, the son of Helios who shows light to men, took to wife fair-cheeked Idyia, daughter of Ocean the perfect stream, by the will of the gods: and she was subject to him in love through golden Aphrodite and bare him neat-ankled Medea."
- Hesiod, Theogony 956