Orbitolina tibetica Cotter, 1929 and Tibetella tibetica Zhang, 1994: Taxonomic review of two ‘lost’ orbitolinids (Foraminifera) from the Lower Cretaceous of Tibet

Orbitolina tibetica was described by Cotter in 1929 from the Lhasa terrane of the Tibetan Himalaya, presumably from the Langshan Fm. Since Schroeder (1963), this species has been mainly included in the synonymy of Palorbitolina lenticularis (Blumenbach, 1805). New and detailed images from the type material of O. tibetica reveal that the illustrated specimens in the original description are undiagnostic except one axial section showing the megalospheric embryo, designated herein as lectotype. This section shows that O. tibetica Cotter, 1929 is identical to Mesorbitolina parva (Douglass, 1960) thus becoming its senior synonym and reinstating the new combination Mesorbitolina tibetica (Cotter, 1929) introduced by Zhang (1982, 1994). Consequently, the type-level of M. tibetica (Cotter) cannot be late Barremian-early Aptian, but has to be late Aptian. Tibetella tibetica Zhang, 1994 from the Albian Langshan Fm. with its tripartite embryo is redescribed and also reassigned to Mesorbitolina Schroeder, 1962. As there is neither a junior nor a senior synoym for this new combination, Mesorbitolina zhangi nomen novum is proposed as a replacement name for Tibetella tibetica Zhang, 1994 to avoid a secondary homonymy with M. tibetica (Cotter, 1929).