The fact that the periproct is supramarginal and there are no gonopores indicates that this is based on a juvenile. The peripetalous and subanal fasciole, together with the fact that the labral plate is relatively short indicates this belongs to the Brissidae.
Clark, H. L. 1939. A remarkable new genus of sea-urchin (Spatangidae). Allan Hancock Pacific Expeditions 2, 173-176.
Clark, H. L. 1948. Report on the Echini of the warmer Eastern Pacific, based on the collections of the Velero III. Allan Hancock Pacific Expeditions 8 (5),