The Echinoid Directory

• Test ovate in outline with faintly concave anterior; short truncate posterior face. Depressed in profile with convex upper and lower surfaces.
• Apical disc ethmolytic with two gonopores (anterior genital plates lacking gonopores). Positioned centrally.
• Anterior ambulacrum faintly sunken aborally; groove continuing to peristome; pore-pairs miniscule.
• Paired ambulacra petaloid; anterior petals extending most of the way to the ambitus; weakly depressed with narrow interporal zone. Posterior petals a little shorter but also extending most of the distance to the ambitus.
• Peristome small and circular; a little removed from the anterior border and facing largely downwards.
• Labral plate small and longitudinally elongate; extending to third ambulacral plate only. Separated from sternal plate 5.b.2 by ambulacral plates 3 and 4. Sternal plate 5.b.2 large and asymmetric, plate 5.a.2 offset behind and only slightly smaller; subsequent plating biserial.
• Periproct posterior and moderately large.
• Peripetalous fasciole passes around the base of the petals.

Upper Palaeocene, Somalia.

Pericosmus gregoryi Currie, 1927, p. 430, by original designation.

• Only the type species.

Spatangoida, Hemiasterina, Somaliasteridae.

Monotypic.

This taxon resembles Brightonia and Iraniaster in having a disjunct plastron. However, Iraniaster differs in having a ethmophract apical disc with four, not two gonopores. The apical disc of Brightonia is also ethmophract, not ethmolytic, and the labrum extends to only the second ambulacral plate.

Kier, P. M. 1957. Tertiary Echinoidea from British Somalia. J. Paleont. 31, 839-902.

Jeffery, C. H. 1999. A reappraisal of the phylogenetic relationships of somaliasterid echinoids. Palaeontology 42, 1027-1041.