BORYSTHENES was a River-God of Skythia, in north-eastern Europe (modern Ukraine).
The Borysthenes River is the Dneiper which flows south across the steppe into the Black Sea. The most important neighbouring rivers were the Istros (Danube) in the west, and Tanais (Don) in the east.
|Presumably OKEANOS & TETHYS
|THOAS (Antoninus Liberalis 27)
Antoninus Liberalis, Metamorphoses 27 (trans. Celoria) (Greek mythographer C2nd A.D.) :
"Iphigeneia she [Artemis] carried off far away from Greece, to the Sea of Pontos [i.e. the Black Seea] with its welcoming name of Euxinos, to Thoas son of Borysthenes [i.e. the River Dnieper]. She called the tribe of nomads there Taurians because a bull (tauros) had appeared instead of Iphigeneia on the altar."
- Antoninus Liberalis, Metamorphoses - Greek Mythography C2nd A.D.