Belongs within: Cidaroida.
The Histocidarinae are a group of cidaroid urchins known from the Jurassic to the present (Fell 1966).
Characters (Fell 1966): Primary tubercles strongly crenulate. Primary spines cylindrical, not clavate; either smooth or thorny. Secondary spines elongate, erect, more or less flattened, but not squamiform. Pores nonconjugate, conspicuous wall separating inner from outer pore. Tridentate pedicellariae present, globiferous pedicellariae wanting.
<==Histocidarinae [Histocidarina]F66
|--Poriocidaris Mortensen 1909 [incl. Porocidaris Agassiz 1872 non Desor 1855]F66
| `--*P. purpurata (Wyville Thomson 1874)F66 (see below for synonymy)
|--‘Procidaris’ Pomel 1883 non Pávay 1875F66
| `--*P. edwardsi (Wright 1855) [=Cidaris edwardsi]F66
|--Histocidaris Mortensen 1903F66
| |--*H. elegans (Agassiz 1879) [=Porocidaris elegans]F66
| `--H. mackayiF66
`--Polycidaris Quenstedt 1858F66
|--*P. multiceps (Quenstedt 1858) [=Cidarites multiceps]F66
|--P. legayiF66
|--P. regularis (Münster 1841) [=Eodiadema regulare]SG93
`--P. spinulosaF66
*Poriocidaris purpurata (Wyville Thomson 1874)F66 [=Porocidaris purpurataF66, Cidaris purpurataD05; incl. Poro. gracilis Sladen 1891D05]
*Type species of generic name indicated
References
[D05] Döderlein, L. 1905. Arktische Seeigel. In: Römer, F., & F. Schaudinn (eds) Fauna Arctica. Eine Zusammenstellun der arktischen Tierformen, mit besonder Berücksichtigung des Spitzbergen-Gebietes auf Grund der Ergebnisse der Deutschen Expedition in das Nördliche Eismeer im Jahre 1898 vol. 4 pp. 373–394. Gustav Fischer: Jena.
[F66] Fell, H. B. 1966. Cidaroids. In: Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt U. Echinodermata 3 vol. 1 pp. U312–U339. The Geological Society of America, Inc., and The University of Kansas Press.
[SG93] Simms, M. J., A. S. Gale, P. Gilliland, E. P. F. Rose & G. D. Sevastopulo. 1993. Echinodermata. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 491–528. Chapman & Hall: London.