The Echinoid Directory

Allomma Pomel, 1883, p. 105

[=Alomma Lambert & Thiery, 1911, p. 190 (objective)]

Diagnostic Features
  • Test flattened below, weakly domed above.
  • Apical disc large, pentagonal, a little less than half test diameter; plating caducous; presumed monocyclic.
  • Ambulacra straight, plating polygeminate throughout; pore-pairs differentiated, those below the ambitus being small and oblique, those above the ambitus being larger, horizontal and more closely spaced; more or less uniserial throughout forming slight arcs even adorally; no phyllodes. Primary ambulacral tubercle to each plate at ambitus and above; plate compounding acrosaleniid, with all elements reaching the perradius and all overlapped by the primary tubercle at the ambitus. Sharp change below the ambitus to two small subequal tubercles to each plate.
  • Interambulacral plates a little wider than tall; ambital and adapical plates with a single large tubercle, centrally placed, which diminishes in size adapically. Narrow interradial zone of small secondaries and granules widening a little adapically. Below the ambitus plates with two or three small subequal tubercles.
  • A naked interradial zone is present adapically in the interambulacra.
  • Ambulacral and interambulacral tubercles similar in size; perforate and crenulate.
  • Peristome less than half test diameter; strongly sunken. Buccal notches small but clearly marked and with lip. No sphaeridial pits.
  • Spines long and slender, cylindrical, rather fine. Solid and without cortex. Lantern with keeled teeth.
  • Perignathic girdle with auricles fused perradially and with well-developed apophysis.
Cretaceous (Albian - Cenomanian), western Europe.
Name gender neuter
Pseudodiadema normanniae Cotteau, 1863, p. 468 [=Diadema desori Woodward, 1856, p. 8], by original designation.
Species Included
  • A. rhodani (Agassiz, 1840); Lower to Middle Albian, Europe.
  • A. desori (Woodward, 1856); Upper Albian-Cenomanian, western Europe.
  • A. wrighti Smith & Wright, 1993; Cenomanian, England.
Classification and/or Status

Euechinoidea, Calycina, Phymosomatoida, Emiratiidae, Emiratiinae.

Prseumed monophyletic.


The type species is distinguished from more primitive species placed in this taxon by the sharp change in tuberculation that occurs beneath the ambitus (from plates with a single large primary tubercle to plates with multiple small, equal tubercles).  These species were previously attributed to Polydiadema.

Pomel, A. 1883. Classification méthodique et Genera des Échinides vivante et fossiles. Thèses présentées a la Faculté des Sciences de Paris pour obtenir le Grade de Docteur ès Sciences Naturelles 503, Aldolphe Jourdan, Alger, 131 pp.

Smith, A. B. & Wright, C. W. 1993. British Cretaceous Echinoids. Part 3, Stirodonta 2 (Hemicidaroida, Arbacioida and Phymosomatoida, part 1). Monograph of the Palaeontographical Society (publication no. 593, part of vol. 147), 199-267, pls 73-92.