Part S, Echinodermata 1, vol. 1 & 2 , Ch. 2, p. 86 - 267 - Kesling, Robert V.; Durham, J. Wyatt; Macurda Jr., Donald B.; Wanner, Johannes; Beaver, Harold H.; Ubaghs, Georges; Moore, Raymond C.; Fay, Robert O. (Treatise on Invertebrate Paleontology, 1968)