Differs from Pourtalesia in having a much less developed subanal heel. In Pourtalesia the periproct is supraambital, whereas in Spatagocystis it is marginal to inframarginal.
Agassiz, A. 1879. Preliminary report on teh Echini of the Exploring Expedition H. M. S. Challenger Sir C. Wyville Thomson Chief of Civilian Staff. Proceedings of the American Academy of Arts and Science 14, 182-261,
A. Agassiz 1904. Reports on an exploration off the West coasts of Mexico, Central and South America, and off th Galapagos Islands 32, The Panamic deep sea echinoids. Memoirs of Museum of Comparative Zoology, Harvard 31