Belongs within: Cidaroida.
Archaeocidaris is a genus of urchins with a flexible test known from the Carboniferous and Permian (Fell 1966).
Characters (Fell 1966): Test subspherical, probably depressed aclorally and adapically. Amb plates tending to form triads, with irregular enlargement of each successive third plate. Interamb plates in four columns (at least ambitally), interradial series imbricating more or less upon adradial and adradial more or less upon amb series. Primary spines smooth, striate, or spinulose, or with lateral expansions, but without terminal clavate or discoid shaft; cortex reduced (or ?absent), medulla (in some or all) hollow.
<==Archaeocidaris M’Coy 1884 (nom. cons.)B01 (see below for synonymy)
|--*A. urii (Fleming 1828) [=Cidaris urii, *Echinocrinus urii]F66
|--A. aliquantulaF66
|--A. blairiF66
|--A. diadematoides Haude & Thomas 1994B01
|--‘Cidaris’ forbesiana [=*Permocidaris forbesiana]F66
|--A. immanensis Kier 1958SG93
|--A. keyserlingi (Geinitz 1848)B01
|--‘Cidaris’ laevispina [=*Eocidaris laevispina]F66
|--A. nerei (Münster 1839)SG93 [=Cidarites nereiF66, *Palaeocidaris nereiF66]
|--A. ornatus Newberry 1861W77
|--A. rossicaB01
|--A. selwyni Etheridge 1892F71
|--A. trudifer White 1874W77
`--A. wortheni [=*Cidarotropus wortheni]F66
Archaeocidaris M’Coy 1884 (nom. cons.)B01 [=Echinocrinus Agassiz 1841 (nom. rej.)F66; incl. Cidarotropus Pomel 1883F66, Eocidaris Desor 1856F66, Palaeocidaris Desor 1846F66, Permocidaris Lambert 1899F66]
*Type species of generic name indicated
References
[B01] Boczarowski, A. 2001. Isolated sclerites of Devonian non-pelmatozoan echinoderms. Palaeontologia Polonica 59: 1–219.
[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.
[F71] Fletcher, H. O. 1971. Catalogue of type specimens of fossils in the Australian Museum, Sydney. Australian Museum Memoir 13: 1–167.
[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.
[W77] White, C. A. 1877. Report upon the invertebrate fossils collected in portions of Nevada, Utah, Colorado, New Mexico, and Arizona, by parties of the expeditions of 1871, 1872, 1873, and 1874. U.S. Geographical Surveys West of the One Hundredth Meridian 4 (1): 1–219, pls 1–21.