The Echinoid Directory

• Test small, low, oval, greatest width posterior to center; adoral surface depressed towards peristome.
• Apical system very eccentric anteriorly, tetrabasal, with genital plate 2 extending posteriorly separating the posterior oculars.
• Petals slightly developed, short; petal III shorter than others, closing slightly distally. Interporiferous zones equal in width to poriferous zones; outer pore very slightly elongate transversely, inner pore round; conjugate.
• Periproct supramarginal, midway between apical system and posterior margin; elongate longitudinally, in groove that extends to posterior margin.
• Peristome anterior, transversely oval, depressed.
• Bourrelets confined to narrow invaginated rim of peristome.
• Phyllodes slightly developed, single pored; outer series and short inner series developed.
• Buccal pores present.
• Adorally tubercles only slightly larger than adapically.
• Narrow granular naked zone in posterior interambulacrum.

Cretaceous (Albian-Cenomanian), Texas, Colombia.

Echinobrissus angustatus Clark, 1915, p. 69, by monotypy.

• Only the type species included.

Irregularia; Cassiduloida; Apatopygidae.

Subjective junior synonym of Nucleopygus L. Agassiz 1840.

Lambert (1916) differentiated this genus from Nucleopygus on account of its low, short, posterior sulcus and its very small rounded periproct. However, the type species is not significantly different from many representatives of Nucleopygus.

W. B. Clark & M. W. Twichell. 1915. The Mesozoic and Cenozoic Echinodermata of the United States. U. S. Geological Survey Monograph 54, 341 pp., 108 pls.

C. Wythe Cooke. 1946. Comanche Echinoids. Journal of Palaeontology, 20 (3): 193-237, pls 31-34.

C. Wythe Cooke. 1955. Some Cretaceous echinoids from the Americas. U. S. Geological Survey Professional Paper 264-E, 87-112, pls 18-29.

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

Lambert, J. 1916. Revue critique de Zoologie 20, p. 169.