The Echinoid Directory

• Test depressed.
• Apical disc unknown.
• Interambulacra with five plates in a column. Primary tubercles with large mamelon (>40% areole diameter); lowest two imperforate, upper three with small rudimentary perforation; virtually no platform surrounding mamelon.
• Scroibicular circles differentiated; contiguous in column at ambitus; extrascrobicular granules dense and uniform interradially.
• Ambulacral zones weakly sinuous; pore-pairs non-conjugate with a narrow interporal ridge between the two pores. Ambulacral tuberculation uniform throughout, with a primary tubercle and small inner secondary to each plate.
• Peristome about half test diameter.
• No test with spines definitely associated. Attributed spines clavate with short neck and shaft ornamented with dense rows of spinelets.

Middle and Upper Jurassic (Bajocian-Oxfordian), UK and France.

Cidaris honorinae Cotteau, 1880, p. 433, by original designation. Lectotype in the Cotteau collection, Lyon.

• M. honorinae Cotteau, 1880; Upper Bajocian, Lower Bathonian, UK and France.
• M. propinquus (Munster, in Goldfuss, 1829); Oxfordian, Europe.

Cidaroida, Psychocidaridae.

Subjective junior synonym of Tylocidaris.

This taxon has recently been redescribed by Vadet (1991). It is identical to Tylocidaris in test morphology, distinguished from the type species clavigera only by having more consistently perforate mamelons on ambital and adapical plates. As other Cretaceous species such as Tylocidaris velifera also have ambital and adapical tubercles perforate there seems no significant test characters on which to distinguish Merocidaris.

Thiery, P. 1928. Considerations phylogenetiques sur les Cidaridae. Archives de Zoologie experimentale et generale 67, Notes et Revue 4, 179-181.

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