Sellialveolina Colalongo, 1963 is the most primitive rhapydioninid genus known, and it is the only genus of axially compressed alveolinaceans (Rhapydioninidae) present in the Middle Cretaceous Global Community Maturation cycle. Sellialveolina colonized the Tethyan carbonate platforms from the Middle East to the Iberian Peninsula. This work is based on a detailed analysis of the internal structure of Sellialveolina which enabled clarification of its morphostructural features and the phylogenetical and stratigraphical relationships between its species. The basic structure of Sellialveolina consists of a subdivision of the chamber lumen into numerous chamberlets by septula and floors. The chamberlets, placed in the center of the chamber, exhibit a tendency to develop a crosswise-oblique structure. Within the Cenomanian, four Sellialveolina species are identified, and these species replace each other throughout geological time: S. viallii and S. quintanensis n. sp. occur in the lower Cenomanian, S. gutzwilleri n. sp. in the middle Cenomanian and S. drorimensis, in the upper Cenomanian. S. drorimensis topotypes do not support assignment to PseudedomiaHenson, 1948, as previously suggested.