- Test shape depressed in profile, circular to pentagonal in outline; plating imbricate, with ambulacral plates extending far beneath interambulacral plates.
- Apical disc monocyclic and relatively small with five larger genital plates and five smaller ocular plates. Genital plates with up to 12 gonopores arranged in an arc. One genital plate densely perforated by hydropores.
- Ambulacra biserial throughout; narrow adapically but expanded adorally. Aboral plates small and with small, unspecialized pore-pair; adoral plates much larger and wider; dominated by large, subcircular pore-pair with prominent rim.
- Internally ambulacral plates without perradial flanges.
- Interambulacral zones wider than ambulacral zones; composed of up to 10 columns of rhomboidal plates arranged in rows; imbricating strongly adapically and adradially.
- Small perforate tubercle with weakly sunken areole present on most interambulacral plates; fine scattered granules also present.
- Lantern present; structure unknown.
- Spines short and simple.
Carboniferous, Europe & USA.
Hyattechinus beecheri Jackson, 1912, p. 291, by original designation.
- H. beecheri Jackson, 1912; Lower Carboniferous, USA.
- H. pentagonus Jackson, 1912; Waverley Group, Carboniferous, USA.
- H. laudoni Kier, 1965; Lodgepole Formation, Montana, USA.
- H. dixoni Hawkins, 1935; Lower Carboniferous, Wales.
- H. toreumaticus Hawkins, 1935; Lower Carboniferous, Wales.
- H. elegans Jackson, 1929; Tournasian, Belgium.
- H. rarispinus (Hall, 1868); Waverley Group, Carboniferous, USA.
|Classification and/or Status
Stem group Echinoidea; Proterocidaridae.
Distinguished from Proterocidaris, which has similar enlarged adoral pore-pairs, in having its ambulacral plating strictly biserial throughout. Perischodomus has biserial ambulacra adapically, but multiserial ambulacra adorally.
Jackson, R. T. 1912 Boston Society for Natural History Memoirs 7, p. 296, pl. 24, fig. 4, pl. 25, figs 1, 2.
Jackson, R. T. 1929. Palaeozoic Echini of Belgium. Memoires du Musee Royal d'Histoire Naturelle de Belgique 38, 1-96.
Kier, P. M. 1965. Evolutionary trends in Paleozoic echinoids. Journal of Paleontology 39, 436-465, pls 55-60.