The Echinoid Directory

Tetragramma Agassiz, 1838, p. 4

[=Acanthechinopsis Gregory, 1906, p. 219, type species Acanthechinopsis humei Gregory, 1906 (=Tetragramma variolare Brongniart, 1822); = Hexagramma Pomel, 1883, p. 102, type species Tetragramma planissimum Agassiz, 1840.]

Diagnostic Features
  • Test flattened below and above; ambitus rounded.
  • Apical disc large, pentagonal, a little less than half test diameter; plating caducous; presumed monocyclic.
  • Ambulacra straight, plating trigeminate adorally but quadrigeminate adapically; pore-pairs uniform and undifferentiated; at ambitus more or less uniserial, becoming biserially offset adapically and developing into short phyllodes adorally. Primary ambulacral tubercle to each plate; plate compounding diadematid, with all elements reaching the perradius and overlapped by the primary tubercle at the ambitus.
  • Interambulacral plates a little wider than tall; plates with two or three subequal primary tubercles on ambital plates, fewer adapically and adorally (and in juveniles); interradial zone broad and virtually naked adapically; scattered granules and small secondaries elsewhere.
  • Ambulacral and interambulacral tubercles similar in size; perforate and crenulate.
  • Peristome about half test diameter; buccal notches small and well defined. No sphaeridial pits.
  • Spines short, about half test diameter; tapering distally and without cortex. Circular in cross-section.
  • Lantern stirodont with keeled teeth.
Distribution
Upper Jurassic (Oxfordian) to Upper Cretaceous (Turonian), western Europe, Middle East, North Africa, North & South America.
Name gender neuter
Type
Cidarites variolare Brongniart, in Cuvier & Brongniart 1822, p. 84, by subsequent designation of Lambert & Thiery, 1910, p. 187.
Species Included
  • T. variolare (Brongniart 1822); Cenomanian, Europe, North Africa
  • T. tenerum Smith & Rader 2009; Lower Albian, Texas, USA
  • T. besairiei Lambert, 1933; Turonian, Madagascar, India
  • T. planissimum Agassiz, 1840; Kimmeridgian, Europe
Many other species
Classification and/or Status
Phymosomatoida, Emiratiidae, Diplopodiinae.
Remarks
Distinguished from Diplopodia only by having two or more subequal primary tubercles on interambulacral plates.

Agassiz, L. 1838. Monographies d'Échinodermes vivants et fossiles. Première monographie: Des Salénies. Petitpierre, Neuchâtel, 32 pp., 5 pls.