McNamara distinguished this taxon from Hemiaster because of its flush anterior ambulacrum and its narrow, poorly developed and only slightly depressed petals. In addition it has a shorter labrum, extending to ambulacral plate 2, and symmetrical sternal plates. In all of these features it resembles Bolbaster and is here treated as a synonym.
Neraudeau (1994) distinguished Psephoaster from Bolbaster stating that the anterior part of the petals in Psephoaster have atrophied pore-pairs. This is, however, a character developed in almost all hemiasterids to a greater or lesser extent.
McNamara, K. J. 1987. Taxonomy, evolution, and functional morphology of southern Australian Tertiary hemiasterid echinoids. Palaeontology 30, 319-352.
Neraudeau, D. 1994. Hemiasterid echinoids (Echinodermata: Spatangoida) from the Cretaceous Tethys to the present-day Mediterranean. Palaeogeography, Palaeoclimatology, Palaeoecology 110, 319-344.