Pleijel (1998:122) discusses the names Psamathe and Kefersteinia. The 2nd is subjective synonym of the first, which is valid, not a junior homonym. Pleijel (p.159) states that Kefersteinia is an objective synonym of Psamathe, but this seems a misinterpretation as they are not based on the same types. Their types are synonyms as subjective synonyms, based on worms originally collected from different places and times. Thus because future work could in theory reinstate Psamathe cirrhata out of subjective synonymy the genera could not be objective synonyms. Kefersteinia was not a replacement name for Psamathe.
Pleijel, Fredrik 1998. Phylogeny and classification of Hesionidae (Polychaeta). Zoologica Scripta, 27(2): 89-163, 38 figures, 7 tables.