The Echinoid Directory

Merriamaster Lambert, 1911, p. 64

[=Orchoporus Lambert & Thiery, 1914, p. 293, type species Orchoporus koehleri (=Scutella perrini Weaver, 1908); Twitchellia Lambert & Thiery, 1916, p. 171, type species Astrodaspis merriami Clark & Twitchell 1915 ]

Diagnostic Features
  • Test small and ovate, flattened in profile with rounded margins.
  • Apical disc with four gonopores, slightly posterior of centre.
  • Petals moderately well developed; anterior three petals longer than the posterior pair.
  • Basicoronal circlet pentastellate, with interambulacral plates projecting.
  • Paired interambulacra disjunct on oral surface, separated by first pair of post-basicoronal ambulacral plates.
  • Periproct opening submarginal, bounded by second and third post-basicoronal paired interambulacral plates.
  • Internal butressing poorly developed; composed of radial struts plus a few branching lamellae.
  • Food grooves bifurcating immediately after basicoronals and extending onto aboral surface around posterior in large individuals.
Pliocene, Pacific coast of the USA.
Name gender masculine
Scutella perrini Weaver, 1908, by original designation.
Species Included
  • M. perrini (Weaver, 1908); Pliocene, California, USA.
  • M. weaveri Durham & Morgan 1978; Pliocene, California, USA.
  • Other species may be included (see Durham, 1978, p. 285).
Classification and/or Status

Clypeasteroida, Scutellina, Scutellidea, Scutellidae.

Subjective junior synonym of Dendraster L. Agassiz, 1847.


There are no plating differences between this taxon and the type of Dendraster, and many of the cited differences (more rounded ambitus, simpler food grooves, less developed internal buttressing) seem to be related to the small size of Merriamaster species. Merriamaster does differ from the type species of Dendraster in having somewhat less well-developed internal buttressing at comparable sizes and in having finer bands of interradial tubercles aborally. Whether these are sufficient to merit generic separation is arguable.

J. W. Durham, 1978. Polymorphism in the Pliocene sand dollar Merriamaster (Echinoidea). Journal of Paleontology 52, 275-286.

Lambert, J. 1911. Revue critique de Paleozoologie 15, p. 64.