The Echinoid Directory

• Test cordate with modest frontal sulcus running from apex to peristome.
• Apical disc ethmolytic, with 3 gonopores (no gonopore in genital plate 2); anterior of centre.
• Anterior ambulacrum narrow and sunken adapically. Pore-pairs uniserial and small adapically.
• Other ambulacra with parallel-sided and sunken petals. Petals ending just over half-way to the ambitus.
• Periproct towards top of short vertically-truncate posterior face; transverse.
• Peristome ovate to kidney-shaped with labral plate projecting to more or less cover the opening.
• Plastron wide and fully tuberculate; episternals and sternals form flat surface. Episternal plates subquadrate and a little offset.
• No primary tubercles differentiated. Aboral tuberculation fine and dense.
• Peripetalous and marginal fascioles developed; not merged. Peripetalous fasciole deeply indented behind anterior petals.

Miocene, South Australia.

Megalaster compressus Duncan, 1877, p. 62, by original designation.

• Only the type species.

Spatangoida, Paleopneustina, Paleopneustidea, Pericosmidae.

Subjective junior synonym of Pericosmus Agassiz, 1840.

Duncan established this genus on the basis of a species from the Miocene of the Murray River, South Australia. The type was redescribed along with better material by McNamara & Philip 1984.

Duncan, P. M. 1877. Quarterly Journal of the Geological Society 33, p. 61.

McNamara, K.J. & Philip, G.M. 1984. A revision of the spatangoid echinoid Pericosmus from the Tertiary of Australia. Records of the Western Australia Museum 11, 319-356.