The Echinoid Directory

• Test small, moderately inflated, subcircular to ovoid, greatest width and height posterior to centre, with a depressed adoral surface and distinct adoral swelling of interambulacra 1 and 4.
• Apical system central, monobasal, with four gonopores that show sexual dimorphism.
• Ambulacra narrow, simple, nonpetaloid, with a row of small single pores in each half ambulacrum.
• Peristome anterior, transversely oval.
• Periproct supramarginal, longitudinally oval in a long and deep anal sulcus.
• Phyllodes well developed, expanded, with a distinct inner and outer series in each half ambulacrum; four or five pores in each outer series, two or three in each inner series.
• Bourrelets well developed, tooth-like; basicoronal plates longer than wide.
• Buccal pores present.
• Tubercles small, evenly distributed.

Early Miocene of South Australia.

Actapericulum bicarinatum Holmes, 1995, p. 120; by original designation.

• A. bicarinatum Holmes, 1995; Early Miocene, South Australia.

Irregularia; Cassiduloida; Faujasiidae; Stigmatopyginae.

Monotypic.

Actapericulum has very well developed tooth-like bourrelets, broadened phyllodes with a distinct inner and outer series in each half-ambulacrum, with four or five pores in each outer series, two or three in each inner series. These characters are more characteristic of the Faujasiidae than the Neolampadidae to which Holmes (1995) assigned his genus. The lack of petal development is a neotenic character, which may relate to the small size of specimens of the type species. The supramarginal position of the periproct determines that this genus should be assigned to the subfamily Stigmatopyginae.

F. C. Holmes. 1995. Australian Tertiary Neolampadidae (Echinoidea): A review and description of two new species. Proceedings of the Royal Society of Victoria, 107 (2), pp. 113-128.