The Rhine Maidens are the sisters who cavort in myth-laden currents to get the action moving in Wagner’s Ring cycle — and then return at the end as everything that has happened gets washed away by those same waters. Throughout centuries, the Rhine has been a central metaphor for Germans, and it informs a number of the selections on this delicious album of songs for women’s choir from 19th-century Germany. It was a favorite medium at the time, and many of the greatest mainstream composers wrote works for such ensembles. The repertoire reaches its summit in Brahms’ Four Songs (Op. 17) for women’s choir, two horns, and harp, which shines here in a gripping interpretation. The Bordeaux-based Ensemble Pygmalion, directed by Raphaël Pichon, specializes in historically informed performance, and the timbre of period horns makes a telling difference here compared to other recorded readings. That set is nearly rivaled by Schubert’s famous Ständchen, for women’s choir and solo mezzo-soprano (here Bernarda Fink). Works by Schubert and Schumann take turns in the playlist, along with other selections by Brahms, mostly “as written” but sometimes in winning adaptations, as in a Brahms song about horns that here is actually recast for horn quartet. Pichon includes some interesting but rarely heard canons by these composers, and Wagner’s Rhine Maidens make two appearances to wrap the whole thing in their gauzy veils.