(Here's a pair of costumes for two sisters or friends that's in the same general category as the mermaid, sea maiden, and water spirit previously described, though considerably simpler in ornamentation.)
The 1896 description:
Suitable dresses for two sisters; both would wear green and white tulle dresses and veils. For salt water, these would be trimmed with coral, seaweeds, and shells; the other with water-lilies and grasses.
The 1880 and 1887 descriptions specify green and white evening dresses with white tulle veils but are otherwise identical to the later one.
Holt, Ardern. Fancy Dresses Described, 2nd Edition, Illustrated. London: Debenham & Freebody, 1880.
Holt, Ardern. Fancy Dresses Described, 5th Edition. London: Debenham & Freebody, 1887.
Holt, Ardern. Fancy Dresses Described, Sixth Edition. London: Debenham & Freebody, 1896.
The 1896 edition of Holt may be found online at the University of Wisconsin Digital Collections.