Species differentiation within the genus Mesorbitolina Schroeder 1962 is primarily based on the general structure of the megalospheric embryo and its biometrics. The taxonomy of three taxa, namely Mesorbitolina texana (Roemer 1849), Mesorbitolina subconcava (Leymerie 1878) and Mesorbitolina pervia (Douglass 1960) is complicated due to differing species concepts between authors, and, in the case of the first two named, by missing type designations in the original descriptions as well as disagreements with respect to their type-localities. Herein, it is demonstrated that M. pervia is the junior synonym of Mesorbitolina birmanica (Sahni 1937) due to priority reasons, both taxa characterized by a similar-sized plano-convex protoconch. Some concepts of M. texana and M. subconcava can also be placed in M. birmanica, but not those as defined by lectotypes. Published data for M. birmanica suggest a late Aptian (late Gargasian) to early (? late) Albian age and a cosmopolitan distribution. Mesorbitolina texana appears slightly earlier in the late Aptian persisting into the middle Albian, and a distribution ranging from the southern USA to the Middle East.
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