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Genus Omphalocyclus Bronn
Type species – Omphalocyclus macropora (Lamarck, 1816).
Omphalocyclus macropora (Lamarck, 1816)
Pl. 2, fig. 3.
Description – Test biconcave to discoidal, centrally depressed, with the thickest part at 67 to 75 % of the diameter. Test margin rounded, with a single or double row of apertures. In vertical section the equatorial and lateral chambers are hardly distinguishable. Only one row of lateral chambers is present on each side of the median layer. The test reaches its largest thickness at about two-thirds of the radius, giving it a typical ‘bow-tie’ appearance. Diameter of the macrospheric generation 0.8-2.0 mm, of the microspheric generation up to 5 mm.
Stratigraphy – Omphalocyclus occurs in the top of the Nekum Member and is locally abundant in the Meerssen Member.