- Test of modest size, elliptical; taller than wide. Plates thick.
- Apical disc small, more or less monocyclic (occasionally one or more ocular plates may be just insert). Ocular plates smaller than genital plates. One genital plate larger and densely perforated by hydropores. Two or three gonopores to each genital plate.
- Ambulacra narrow, biserial throughout; weakly imbricate adradially. All elements reaching both adradial and perradial suture. Pore-pairs adradial and small, forming a single series, sometimes offset slightly to left and right.
- Interambulacra with between 4 and 10 columns of thick hexagonal plates, with vertical sutures. No primary tubercles; plates covered in fine, uniform granulation.
- Peristome small, with ambulacral plates continuing over the peristome as well as a few small non-ambulacral plates. A single basicoronal interambulacral plate in each zone.
- Spines fine and short.
- Lantern unknown.
Lower Carboniferous, North America, Europe.
Palaechinus ellipticus McCoy, 1844, p. 172, by subsequent designation of Lambert & Thiery, 1910, p. 119.
- P. sprengi Kier, 1954; Osagean, Canada, USA.
- P. merriami Kier, 1965; early Lower Carboniferous, Nevada, USA.
- P. tetrastichus Kier, 1958; Madison Formation, USA.
- P. quadriserialis Wright, 1865; Lower Carboniferous, Ireland.
- P. elegans McCoy, 1844; Lower Carboniferous, Ireland, Belgium.
- P. ellipticus McCoy, 1844; Lower Carboniferous, Ireland.
- P. visetensis Jackson, 1929; Visean, Belgium.
- P. globulus Jackson, 1929; Tournaisian, Belgium.
- P. canadensis Kier, 1953; Osagean, Canada.
|Classification and/or Status
Stem group Echinoidea; Palaechinidae.
Presumably paraphyletic by exclusion of all Palaechinidae with more complex ambulacral plating.
This genus comprises all Palaechinidae that have uniserial, simple ambulacral plating. Some species, such as P. quadriserialis have an ambulacral structure verging towards that of Maccoya where every second ambulacral plate is wedge-shaped, narrowing towards the adradial suture. Distinguished from Porechinus by having smaller and more obviously adradial pore-pairs, but otherwise very similar.
McCoy, F. 1844. A synopsis of the characters of the Carboniferous Limestone fossils of Ireland. Dublin, 207 pp., 29 pls.
Kier, P. M. 1958. New American Paleozoic echinoids. Smithsonian Miscellaneous Collections 135(9), 26 pp. 8 pls.
Kier, P. M. 1965. Evolutionary trends in Paleozoic echinoids. Journal of Paleontology 39, 436-465, pls 55-60.