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Polyplacidia Poretskaya, 1968, p. 287-289

Diagnostic Features	Apical disc small, plating hemicyclic with oculars I and V exsert; madreporite larger than other plates Ambulacral zones rather broad; plating trigeminate; style of plate compounding not certain but with lowest of three elements the largest.  Primary tubercles somewhat irregularly developed, with outer and inner tubercle columns developed at ambitus Interambulacral plates wide with up to four subequal tubercles in a row.  Tubercles small, crenulate and imperforate. Peristome relatively small Spines and lantern unknown
Distribution	Eocene, Armenia
Type	P. armenica Poretskaya, 1968, p. 290, by original diagnosis
Species Included	P. armenica Poretskaya, 1968, p. 290; Eocene, Armenia.
Classification and/or Status	Echinacea; unnamed family (triplacidiids) Monotypic
Remarks	Originally placed in the Phymosomatidae but ambulacral plating argues against this. Close to Triplacidia, differing in having a rather irregular distribution of ambulacral tubercles to its compound plates. Poretskaya, E. S. 1968. Polyplacidia artenica - a new genus and species of sea urchin from south-western Armenia. Ezhegodnik Vsesouznoe Paleontologicheskoe Obschchestvo 18, 286-297, figures 1-6, plates 1-2. [in Russian]