Origine, évolution et systématique de Praechubbina n. gen., foraminifères alveolinacea du crétacé supérieur du Guatemala et du Mexique

The sub family Chubbininae is represented by many taxa known from the shallow campanian-maastrichtian carbonate platforms of south-east Mexico and Guatemala. The structure of this group, together with the origins of the genus Chubbina, can be understood through the description of 6 new species. One of them, Pseudonummoloculina pecheuxi n. sp., with typical Miliolid features (devoid of any internal partitions), seems to be the common ancestor of the others. It is especially that its aperture, a slit with a crenellated margin, give birth to the multiple rows of rounded apertures distinctive of the sub family, of which the new genus Praechubbina belongs. The 5 other new species, together with « Borelis cardenasensis Barker and Grimsdale, are gathered in the new genus. One of them, Praechubbina breviclaustra n. sp., displays a link between Pseudonummoloculina pecheuxi n. sp. and the five congeneric new species: its aperture, originally a slit with a crenellated margin, changes into rows of several rounded openings; the same species shows the advent of a faint partitioning. The other species, P. cardenasensis (Barker et Grimsdale), P. compressa n. sp., P. obesa n. sp., P. ovoidea n. sp. et P. streptospira n. sp. share the same apertural features; they display a large range fvarious of shell coiling and endoskeletal organisation (inclusive of floors emergence) not connected to the proloculus size. The new genus corresponds to a very rich plexus in which the various species of Chabbina takes roots.