The Echinoid Directory

• Test small (<5 mm) and flattened. Margins thick and rounded; lower surface pulvinate.
• Internal support arrangement of 10 L- or Y-shaped struts.
• Apical disc central with four gonopores. Deeply sunken in females and with sexual dimorphism in gonopore size. Several hydropores scattered over disc.
• Petals hardly developed - three pore-pairs per column only.
• Periproct opening on oral surface towards posterior margin.
• Food grooves absent.
• Peristome central.
• Ambulacral and interambulacral plating not recorded.

Pliocene, Beibuwan, Guangxi, China.

Tetradiella sinica Liao & Lin, 1981, by original designation.

Only the type species.

Clypeasteroida; Scutellina; Laganiformes; Laganidae; subfamily uncertain

Monotypic.

Differs from Pentedium in having four rather than five gonopores and more numerous hydropores. Interambulacral plating is not recorded, and so it is not even certain that this is a laganiform. Assuming it is, the branching internal supports show that this taxon is a laganid, however, it is not possible to place this in either of the subfamilies with any confidence on current information.

Liao, Y-L & Lin, C-H 1981. A new echinoid with sexual dimorphism from the late Tertiary deposits of Beibuwan, Guangxi. Acta Palaeontologica Sinica 20, 482-484, pl. 1.