F. S. Conant, Mem. Johns Hopkins Univ. iv. 1, 1898.
Kishinouye, Journ. Coll. Sci. Tokyo, xvii. 7, 1902.
A discussion of the classification of this order occurs in Vanhöffen, "Acrasped. Med. d. deutschen Tiefsee Expedition," iii. 1902, p. 49.
The Periphyllidae constitute Haeckel's order Peromedusae.
A stage in development before the formation of the sub-umbrellar cavity, but subsequent to the formation of the first tentacles, is regarded as homologous with the Scyphistoma stage of other Scyphozoa.