The genus Omphalocyclus Bronn is a Late Cretaceous orbitoidal larger foraminifera, usually considered as a marker for the Maastrichtian. Herein we describe Omphalocyclus specimens from the upper part of the Qahlah Formation in North Oman, probably representing the most primitive developmental stage of the genus in the Tethys. The studied specimens are characterized by having delicate discoidal, biconcave tests with a notably small, ‘trilocular’ embryonic apparatus and a few (usually 2) epi-embryonic chamberlets. The embryonic wall in some specimens is thin and hardly discernible as a separate morphological entity compared to following chamberlets. Duplication of the annular series of chamberlets in the equatorial plane (equatorial layer), a characteristic morphological feature of the genus, is observed at a late ontogenetic stage. After comparison of these specimens with specimens of type-species O. macroporus (Lamarck) from the Simsima Formation in Oman and previously described species (e.g., O. anatoliensis Özcan, O. cideensis Özcan, O. maldonensis Gunter, Robinson, Mitchell), a new species, O. omanensis sp. nov. is established. The stratigraphic distribution of the genus is updated, and a tentative phylogenetic scheme is proposed. The upper part of the Qahlah Formation in the Buraymi region is assigned to the upper Campanian based on the recognition of calcareous nannofossils Zones CC22b and CC23a and the occurrence of Orbitoides medius (d’Archiac).

属Omphalocyclus Bronn是晚白垩orbitoidal较大有孔虫，通常被认为是用于马斯特里赫特的标记。在此我们描述Omphalocyclus来自阿曼北部Qahlah组上部的标本，可能代表了特提斯属最原始的发育阶段。所研究的标本的特征在于具有细小的盘状双凹检验，并带有明显较小的“三眼”胚胎装置和几个（通常为2个）胚外胚乳小室。与随后的小室相比，某些标本中的胚壁薄且难以辨别为单独的形态实体。在后期的个体发育阶段，观察到了在赤道平面（赤道层）中环形小室的重复，这是该属的特征形态特征。在将这些标本与大孔O.types标本进行比较之后（Lamarck）来自阿曼Simsima组和先前描述的物种（例如O. anatoliensisÖzcan，O。cideensisÖzcan，O。maldonensis Gunter，Robinson，Mitchell），新物种O. omanensis sp.。十一月 成立。更新了属的地层分布，并提出了一种初步的系统发育方案。根据对钙质纳米化石区CC22b和CC23a的认识以及中天轨道（d'Archiac）的出现，将Buraymi地区的Qahlah组的上部分配给上坎潘期。