The Echinoid Directory

Dixonia Wagner & Durham, 1964, p. 170

Diagnostic Features
  • Small; reaching no more than 15 mm in diameter.
  • Apical disc with five subequal genital plates, all of which are covered in hydropores.
  • Ambulacra simple near the apex, becoming trigeminate at the ambitus and adorally.
  • Upper and lower elements in each triad compound plate are small demiplates occluded from the midline.
  • Narrow blade-like ridges run internally from the peristome to the ambitus along the adradial margins of interambulacral zones.
  • Peristome small and central.
  • Periproct always oral and relatively small.
  • Inflated and subconical in profile.
  • Aboral plates with granules arranged into rows leaving wedge-shaped naked zones.
Distribution
Late Cretaceous (Late Cenomanian to Coniacian), western Europe.
Name gender feminine
Type
Discoidea minima Desor, 1842, by original designation.
Species Included
  • Only the type species.
Classification and/or Status

Holectypoida, Holectypidae, Discoidinae.

Subjective synonym of Camerogalerus Quenstedt, 1873

Remarks

Dixonia was established for Discoidea minima, which differs from Discoides in having a fifth gonopore, a more rounded profile and a somewhat smaller periproct. Although in size and general appearance it resembles Discoides, its apical disc is identical in structure to that of Camerogalerus, as is its ambulacral plate compounding. Like Camerogalerus it has sharp, blade-like internal partitions. All three characters point to closer relationship with Camerogalerus cylindricus than with Discoides subuculus.

Smith, A. B. & Wright, C. W. 1999. British Cretaceous Echinoids. Part 5, Holectypoida, Echinoneoida. Palaeontographical Society Monographs, 343-390, pls 115-129.