The Echinoid Directory

• Periproct large, forming a keyhole shaped opening on the aboral surface and extending almost to the ambitus.
• Apical disc transverse with anterior ocular plates separated from the periproct. Anterior border of periproct formed of genital plate 2 plus posterior oculars.
• Ambulacra straight, with uniserial pore-pairs; pore-pairs undifferentiated. Plating trigeminate adorally, with primary tubercles over pairs of elements.
• Peristome large, central, with prominant buccal notches; slightly wider than long.
• Tuberculation coarse and dense.

Late Cretaceous (Cenomanian) of France.

Pygaster truncatus Desor, 1857, explanation to plate 22, by original designation.

Only the type species was included when the genus was erected. Vadet et al. (2001) added the Oxfordian species laganoides.

Holectypoida, Pygasterina, Pygasteridae

A subjective junior synonym of Pygaster Agassiz, 1836

Desor (1857) figured and named the type species and, in a footnote to the explanation of plate 22, stated that Cotteau was going to make this the type species of a new genus Macropygus. However, when Cotteau eventually described the species (Cotteau & Triger 1859, p. 176 in Cotteau & Triger 1855-69), he had changed his mind and he placed the species truncatus in the genus of Pygaster. The genus was, however, validly designated by Pomel (1883, p. 76), differentiated from Pygaster by its slightly elliptical peristome. Vadet et al. (2001) also retained the genus, adding the Oxfordian species Pygaster laganoides Agassiz, 1839 and distinguishing it from Pygaster by its coarser and more densely packed tubercles, its wider ambulacra and narrower interambulacral zones.

Cotteau, G. & Triger, J. 1855-1869. Echinides du Departement de la Sarthe. J.B. Balliere et fils, Paris.

Vadet, Remy, N. & Wille, E. (2001). Echinides du Corallien des Ardennes. Memoires de la Societe Academique du Boulonais. Serie Histoire naturelle 21, 52 pp.