The Echinoid Directory

Leptarbacia Clark, in Clark & Twitchell, 1915, p. 53

[=Sinaiopsis Smith, Racey & Simmons, 1990, p. 54, type species Pedina sinaica Agassiz & Desor, 1847 ]

Diagnostic Features
  • Test small (20 mm) depressed above, flattened beneath.
  • Apical disc small, hemicyclic with both posterior oculars exsert. Periproct circular, with smooth rim.
  • Ambulacra straight, moderately wide at ambitus. Plate compounding pedinopsid style, with one large element and three demiplates (occasionally two demiplates). Small primary tubercle to each compound plate adjacent to the pore zone.
  • Pore pairs more or less uniserial in each column, becoming biserial close to the apex.
  • Interambulacral plates numerous, much wider than tall, bearing three subequal tubercles on subambital plates. Aborally there is just the primary tubercle. Remainder of plate sparsely granular.
  • Tubercles with small perforation and feeble crenulation; ambulacral and interambulacral tubercles of similar size.
  • Peristome circular with moderately sharp buccal notches; about one-third test diameter.
Upper Cretaceous (Cenomanian) USA, Middle East and Arabian Peninsula.
Name gender feminine
Leptarbacia arguta Clark, in Clark & Twitchell, 1915, p. 53, pl. 16, fig. 1, by monotypy.
Species Included
  • Leptarbacia arguta Clark, 1915; Cenomanian, USA
  • L. sinaica (Agassiz & Desor, 1847); Cenomanian, Middle East, Arabian Peninsula
Classification and/or Status

Euechinoidea, Echinacea, unnamed family (pedinopsids).



Close to Pedinopsis but with uniserial pores aborally. Plating quadrigeminate with second element only reaching perradius.

Cooke (1946) redescribed and synonymised it with Micropsis lineatus Clark, 1915, which he figured. He also placed it as a synonym of Diademopsis despite its very different ambulacral plate compounding and crenulate tuberculation.

Cooke, C. W. 1946. Comanche echinoids. Journal of Paleontology 20, 193-236.

Clark, W. B. & Twitchell, M. W. 1915. The Mesozoic and Cenozoic Echinodermata of the United States. Monographs of the United Staes Geological Survey 54, 227 pp., 108 pls.