The Echinoid Directory

• Test moderately depressed and thick.
• Apical disc and peristome plating unknown.
• Interambulacra with 6 or 7 plates in each column.
• Primary tubercles perforate and ambital and adapical tubercles weakly but distinctly crenulate. Adapical tubercles with relatively large mamelon and small (rudimentary) perforation. Areoles circular, incised and non-confluent except close to the peristome.
• Scrobicular tubercles differentiated; extrascrobicular zones covered in dense secondary tubercles.
• Ambulacra narrow, sinuous, the pore zones depressed. Pore-pairs narrow and non-conjugate, the two pores separated by a narrow tubercle. Ambital plates with large contiguous marginal tubercle and smaller inner tubercle.
• Adoral ambulacral tuberculation apparently remains simple (no alternately large and small tubercles), but all specimens of type species relatively small.
• Primary tubercles relatively short and fusiform to clavate. Collar short; short smooth neck; shaft ornamented by relatively dense, beaded ribs, with ribbing distinctly coarser on one side.

Middle Jurassic (Aalenian to Bathonian), western Europe.

Cidaris bradfordensis Wright, 1857, p. 42, by original designation.

• Vadet (1991) included two species when erecting this genus; A. bradfordensis (Wright, 1857) and A. saemanni (Cotteau, 1857).

Cidaroida; Cidaridae stem group.

Subjective junior synonym of Plegiocidaris Pomel, 1883.

The taxon was established by Vadet (1991). He included it within his family Nenoticidaridae characterised by their modestly sized mamelons on interambulacral tubercles and their spines with dense beaded ribs. The absence of alternately large and small ambulacral tubercles distinguish this taxon from Anisocidaris. Compared to Plegiocidaris the spines are less clavate and with a shorter neck, but the ornamentation of the shaft is similar.

Vadet, A. 1991. Revision des "Cidaris" du Lias et du Dogger Europeens. Memoires de la Societe academique du Boulonnais 10, 1-176.