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The Echinoid Directory

Family Tithoniidae Solovjev, 1966, p. 44

Diagnosis

 Stem group atelostomates with:

  • disjunct apical disc, the posterior oculars separated from the remainder of the disc by plates of interambulacra 1 and 4 meeting along the aboral midline
  • ocular plates II and IV large and posterior to anterior genital plates, but bearing gonopores on their distal angles; genital plates 1 and 4 may be present as reduced and imperforate plates.
Range
Middle Jurassic (Callovian) to Lower Cretaceous (Albian); Europe, North Africa.
Remarks
The structure of the apical disc distinguishes this taxon from all other atelostomates other than the pourtalesiid holasteroids. In pourtalesiids the posterior gonopores have also moved anteriorly onto ocular II and IV, but in that clade there is a subanal fasciole.