The Echinoid Directory

Contributed by Andrew Smith, August 2011

Thylechinus Pomel, 1883, p. 91

[?=Tiarotrophus Pomel, 1883, p. 82, type species Cyphosoma schlumbereri Cotteau, 1864; =Orthocyphus Arnaud, 1896, p. 234, type species Cyphosoma pulchellum Cotteau, 1864.

Cenchritechinus Lambert, 1911, was established as a subgenus.]

Diagnostic Features
  • Apical disc moderately large, plating dicyclic and firmly bound to the corona.  Ocular plates small, genital plates large with gonopores at outer point.  Ring of periproctal tubercles on genital plates.  Periproct edge smooth
  • Ambulacral plates trigeminate; pore-pairs uniserial becoming slightly offset close to the peristome. Plate compounding diadematid, with central element the largest and all elements reaching the perradius. Primary tubercle to each compound plate.
  • Interambulacra with single primary tubercle to each plate and with fine, dense and uniform granulation to adradial and interradial sides.  Primary tubercles contiguous in column.
  • Adapical perradial zone in interambulacra sunken as a marsupium in females.
  • All tubercles imperforate and crenulate
  • Peristome slightly sunken and relatively large, with shallow buccal notches.
  • Spines and lantern unknown
Distribution Upper Cretaceous, North Africa.
Name gender masculine
Type Cyphosoma said Peron & Gauthier, in Cotteau, Peron & Gauthier 1881, by subsequent designation of Lambert & Thiery, 1911, p. 214.
Species Included Lambert & Thiery (1911) included a large number of species, but only those with strong sexual dimorphism should probably be included. Pomel (1883) included only Cyphosoma ioudi Peron & Gauthier, 1881 in addition to the genotype.

Tiarotrophus schlumbergi (Cotteau, 1864) probably belongs here.
Classification and/or Status Uncertain
Remarks The diadematoid plate compounding, imperforate, crenulate tuberculation and strong sexual dimorphism with brood pouches makes this an immediately recognizable genus.  However its higher relationships remain problematic and it is left unclassified for the moment. Probably close to Plistophyma (which has very similar tuberculation and plate compounding), but with a fixed apical disc.

Cotteau, G. Peron, A. & Gauthier, V. 1881. Echinides fossiles de l\'Algerie. septieme fascicule. Etage Senonien. G. Masson, Paris, 197 pp., 20 pls.

Pomel, A. 1883. Classification methodique et genera des echinides vivants & fossiles. Thesis presentes a la faculte des sciences naturelles, Academie de Paris. Alger, A. Jourdan.