Fell HB, Regnéll G, Kesling RV, Moore RC, Ubaghs G. Part U, Echinodermata 3, vol. 1 & 2, ch. 2, p. 108-210. InvertebratePaleo [Internet]. 1966 Jan. 1 [cited 2024 Nov. 24];. Available from: https://journals.ku.edu/InvertebratePaleo/article/view/5654