Discussion of the Konstellations

[Koen G]

I wonder... this is just a thought, since your proposed Cetus appears in conflict with the other nymph, could this be someone like Perseus who defeated Cetus by holding up Medusa's severed head and frightened the monster to death or turned it to stone? Could there be a myth combined with a Cetus constellation to cinch down the identification? Cetus is in the Perseus Group (along with Andromeda and Perseus) and the pulling of hair (or snake-like tendrils) in the image might be a reference to holding the severed Medusa head.

JKP, I just wanted to return to this suggestion of yours since I happened to come across an interesting mosaic. It's from a Roman settlement in Portugal, though the exact location may not be too important: these mosaics were almost always based on types, and imitated throughout the provinces.

What is more important is that this image shows that there was a type which uses the exact composition you describe, with the figures in roughly the same position as the VM nymphs. It is certainly a better match for the scene than the previous examples. 

   

Perseus with the head of Medusa & Ketos
Roman mosaic [3rd century CE]
Conimbriga near Coimbra, Portugal -
casa dos repuxos (house of fountains)