THE NYMPHAIIDES were Naiad Nymphs of the river Nymphaios in Paphlagonia (a region of the Black Sea coast of Anatolia).

Quintus Smyrnaeus, Fall of Troy 6. 470 ff (trans. Way) (Greek epic C4th A.D.) :
"Nymphaios' (Nymphaeus') stream, hard by a cave, a wide and wondrous cave: sacred it is men say, unto the Nymphai, even all that haunt the long-ridged Paphlagonian hills, and all that by full-clustered Herakleia dwell. That cave is like the work of gods, of stone in manner marvellous moulded: through it flows cold water crystal-clear: in niches round stand bowls of stone upon the rugged rock, seeming as they were wrought by carvers' hands. Statues of Wood-gods stand around, fair Nymphai, looms, distaffs, all such things as mortal craft fashioneth. Wondrous seem they unto men which pass into that hallowed cave. It hath, up-leading and down-leading, doorways twain, facing, the one, the wild North's shrilling blasts, and one the dank rain-burdened South. By this do mortals pass beneath the Nymphai's wide cave; but that is the Immortals' path: no man may tread it, for a chasm deep and wide down-reaching unto Haides, yawns between. This track the Blest Gods may alone behold."

Sources:

• Quintus Smyrnaeus, Fall of Troy - Greek Epic C4th AD