The Echinoid Directory

• Test small, ovate, anterior margin gently rounded, posterior prolonged, truncated at anal groove.
• Apical system anterior, elongate, adjunct, tetrabasal, with four gonopores. Ocular plates II and IV separated by several complemental plates.
• Ambulacra non-petaloid, poriferous zones narrow, pores oblique.
• Periproct supramarginal , surrounded by plates of the apical system, longitudinal, in deep triangular groove which increases in width towards posterior margin.
• Peristome anterior, higher than wide, oval to subpentagonal.
• Bourrelets absent.
• Phyllodes short, pore-pairs in arcs of three.
• No buccal pores.
• Tubercles slightly larger on adoral surface than on adapical.

Middle Jurassic (Aalenian - Bajocian), western Europe.

Hyboclypus caudatus Wright, 1852, p. 100, by monotypy. Holotype: BMNH E1579.

• Only the type species

Irregularia; stem group Atelostomata

Aulacopygus differs from Hyboclypus in the structure of its apical system. Both have apical discs that are elongate, with complemental plates separating genital plates 1 and 4. However, in Aulacopygus the complemental plates also completely separate oculars II and IV, whereas in Hyboclypus such complemental plates only partially separate oculars II and IV. It is worth noting that Kier (1962, p. 29) did not believe this difference to be of generic significance, particularly as the arrangement and number of complemental plates is variable even within one species.

Barras, C. 2006. British Jurassic irregular echinoids. Monograph of the Palaeontographical Society, 1-168, pls 1-14 (publication number 625).

P. M. Kier 1962. Revision of the cassiduloid echinoids. Smithsonian Miscellaneous Collections 144 (3), 262 pp.