The Echinoid Directory

Clarkiella Lambert, 1916, p. 169

[=Clarkella Lambert, 1920 (non Walcott, 1908) - nomen null. ]

Diagnostic Features
  • Test of medium size, circular in marginal outline, highly inflated, almost as high as long, vertically sided, with a flat adoral surface.
  • Apical system anterior, tetrabasal with four gonopores.
  • Petals well developed, broad, equal, open distally, extending to ambitus; interporiferous zones wide, twice width of poriferous zones. Pores conjugate, outer pores elongated transversely, inner pores circular, ambulacral plates beyond petals with single pores.
  • Peristome slightly anterior, shape unknown.
  • Periproct marginal, low on vertical posterior margin, small, longitudinally elongated.
  • Bourrelets strongly developed, tooth-like (according to Kier, 1962, p. 150).
  • Phyllodes single pored, broad, pores arranged in two series in each half-ambulacrum; eight pores in each outer series, two in each inner series.
  • Buccal pores present.
Upper Cretaceous (Late Maastrichtian) of southeastern USA.
Name gender feminine
Cassidulus hemisphericus Slocum, 1909, p. 7;=Cassidulus conoideus Clark in Clark Twitchell, 1915, p. 80; by subsequent designation of Lambert & Thiery, 1921, p. 369.
Species Included
  • C. hemispherica (Slocum, 1909); Late Maastrichtian, USA.
Classification and/or Status

Irregularia; Cassiduloida; Faujasiidae; ?Faujasiinae.

Subjective junior synonym of Lefortia Cossman, 1901.


Clarkiella is similar to Hardouinia, but differs from the type species of Hardouinia by the position of its periproct, being on a vertical posterior face with almost no anal sulcus, and in having wide distally open petals (Smith & Jeffery, 2000, p. 204).

Clarkiella is very similar to Lefortia, both having tetrabasal apical systems with four gonopores, a marginal periproct situated on a vertical posterior face, and similar phyllode and bourrelet development. The petals of these genera vary slightly, being strongly bowed and very broad in Clarkiella, but narrower and less bowed in Lefortia. Such characters are only likely to be significant at the species level. Clarkiella should therefore be considered a subjective junior synonym of Lefortia Cossman, 1901.

P. M. Kier. 1962. Revision of the cassiduloid echinoids. Smithsonian Miscellaneous Collections, 144 (3) 262 pp.

Lambert, J. 1916. Revue critique de Paleozoologie 20, p. 169.

A. B. Smith & C. H. Jeffery. 2000. Maastrichtian and Palaeocene echinoids: a key to world faunas. Special Papers in Palaeontology, 63, 406 pp.