The Echinoid Directory

Tristomanthus Bittner, 1892, p. 355

Diagnostic Features
  • Test of medium size, oval, posterior slightly truncated, greatest width at centre, greatest height slightly posterior of centre, adoral surface concave, deeply depressed towards peristome
  • Apical system slightly anterior, monobasal, with only three genital pores, no pore left anterior genital plate. Pores show sexual dimorphism (larger in females)
  • Petals equal, open, interporiferous zones same with as poriferous zones. Pores conjugate, with deep conjugation groove, pore pairs widely spaced, outer pore slightly elongated transversely; ambulacral plates beyond petals with single pores
  • Peristome central to slightly anterior, deeply depressed, pentagonal, longer than wide
  • Periproct marginal to slightly supramarginal, longitudinally ovate, within a tube-like anal sulcus
  • Bourrelets strongly developed
  • Phyllodes widened, single pored, with two series in each half-ambulacrum
  • Buccal pores present
  • No naked granular zone in interambulacrum 5 adorally, adoral tubercles only slightly larger than adapical
  • Oligocene of Germany
Name gender masculine
Nucleolites subcarinatus Goldfuss, 1826, p. 142.; by subsequent designation of Lambert, 1906, p. 41.
Species Included
  • T. subcarinatus (Goldfuss, 1826); Oligocene, Germany
Classification and/or Status

Irregularia; Cassiduloida; Neolampadidae

Subjective junior synonym of Studeria Duncan, 1891.


Tristomanthus is very similar to Studeria, the type species of both genera having open petals with deep conjugation grooves, only three gonopores (no pore in left anterior genital plate) that show sexual dimorphism (larger in females), a similarly positioned and longitudinal periproct, a longer than wide peristome, depressed, well developed bourrelets and similar phyllodes (Kier, 1962, p. 144). Tristomanthus should therefore be considered a subjective junior synonym of Studeria Duncan, 1891.

Bittner, A. Uber Echiniden der Tertiars von Australien. Sitz. Ber. Akad. Wien. 101(1), p. 355.

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