The Echinoid Directory

Pileus Desor, 1856, p. 167

Diagnostic Features	Test large, pentagonal in outline, weakly conical in profile with flat oral surface sunken towards peristome. Apical central, tetrabasal with 3 or 4 gonopores (gonopore in genital plate 2 not clear). Genital plate 2 apparently very large and filling almost entire disc. Genital and ocular plates small and marginal; plate boundaries not readily apparent. Periproct supramarginal, separated from apical disc by a large number of interambulacral plates. Hardly depressed with only the slightest of subanal depressions. Ambulacra straight; pore-pairs distinctly larger aborally than orally but not elongate. Pore-pairs irregularly offset in twos or threes forming a rather broad band aborally. All ambulacral elements identical; slender and reaching perradial suture; a double column of primary tubercles is present, the two columns offset so that each overlaps a different set of two or three plates. On oral surface pore-pairs uniserially arranged and each triad associated with a primary tubercle. Interambulacral plates extremely wide and low; bearing multiple subequal tubercles on both oral and adapical surfaces. Primary tubercles perforate and probably crenulate. Peristome small (ca. 12% test diameter), circular and with a sunken, funnel-shaped entrance; central; apparently no buccal notches.
Distribution	Upper Jurassic (Oxfordian), France.
Name gender	masculine
Type	Pygaster pileus Agassiz, in Agassiz & Desor, 1847, p. 146, by monotypy. Holotype: Museum National d\'Histoire Naturelle, Paris B12291.
Species Included	Only the type species.
Classification and/or Status	Holectypoida, Pygasterina, Anorthopygidae. Monotypic; plesiomorphic sister group to Anorthopygus.
Remarks	Distinguished from Galeropygus by the widely separated periproct/apical disc and by the complete absence of pore crowding adorally. Anorthopygus has a similar periproct, differing only in having uniserial pore-pairs aborally. Distinguished from Pygaster in having the periproct oblique and far removed from the apical disc. Desor, E. 1855-1858. Synopsis des échinides fossiles, lxviii + 490 pp., 44 pls. Reinwald, Paris.