This paper deals with the fusulinoidean faunas from several recently found Gzhelian localities of the Cantabrian Zone (Spain). All localities have strata belonging to the Puentellés Formation, a lithostratigraphic unit exposed in the northern part of the Picos de Europa Massifs. Three Ferganites species, including F. obesus sp. nov., and several others belonging to the genera Rauserites, Tumefactus, Triticites?, and Quasifusulina are described. The three Ferganites species belong to a single species group, which is so far only known from the Carboniferous of the Cantabrian Zone.
A comparison of these Cantabrian assemblages with contemporaneous faunas from other Carboniferous areas of western Eurasia shows that forms such as Rauserites cf. R. rossicus and Quasifusulina aff. Q. longissima ultima are either identical or closely related to species that were probably widespread in the paleo-equatorial part of Eurasia. Other elements (e.g., Ferganites ex gr. F. obesus, Tumefactus ex gr. Tu. expressus, Triticites? aff. Tr.? gusanicus) had a much more restricted geographic distribution and occurred only in the western part of the Paleo-Tethys. The assemblages are thus correlated with the lower Gzhelian of the Russian Platform.
The fusulinoidean faunas studied demonstrate that the westernmost part of the Paleo-Tethys was still characterized by marine deposits in Gzhelian times. Apparently, the Cantabrian Zone had close affinities with the Carnic Alps and Central Asia and, like these areas, it was part of the Late Carboniferous (Pennsylvanian) Paleo-Tethyan province.