Ubaghs, Georges, J. Wyatt Durham, and K. E. Caster. 1968. “Part S, Echinodermata 1, Vol. 1 & 2 ,Ch. 5, P. 565 - 637”. Treatise on Invertebrate Paleontology, January. https://doi.org/10.17161/dt.v0i0.5638.