Forbes, "A History of British Starfishes and other animals of the class Echinodermata," 1841, p. 23.
Simroth, "Anatomie und Schizogonie der Ophiactis virens," Zeitschr. wiss. Zool. xxvii. 1876, p. 452.
Cuénot, "Études Morphologiques sur les Echinodermes," Arch. Biologie, xi. 1891, pp. 568 et seq.
This type of mouth-frame is represented in Fig. 215, A, by a figure of Ophioscolex, which belongs to the Streptophiurae.
"Asteriden und Ophiuriden aus dem Silur Böhmens," Zeitschr. der deutschen geol. Ges. lv. 1903, pp. 106-113 (Protokolle).