Abstract

This paper discusses the classification and evolutionary trends of the late Turonian-early Campanian genera Gavelinella and Stensioeina from western Ukraine, including the definition of five Gavelinella lineages (G. ammonoides, G. stelligera, G. vombensis, G. pertusa, and G. clementiana) and two Stensioeina lineages (S. exsculpta and S. perfecta). The latter two differ from each other in test shape, umbilical arrangement, and stratigraphic ranges. Older forms of S. exsculpta possess an umbilicus partially covered by triangular flaps extending from the umbilical parts of the chambers (type-X ornamentation), whereas the umbilicus in younger forms is partially covered by undulating outgrowths extending from the surface of the test (type-Y ornamentation). Changes in the Stensioeina perfecta lineage include an increased test thickness and an umbilical area characterized by widening and joining of chamber flaps into an umbilical plug. Protostensioeina n. gen. is proposed to accommodate species characterized by the lack of features typically observed in Stensioeina, such as spiral-side ornamentation consisting of curved, limbate sutures, strongly elevated in somewhat irregular, curly ridges, resulting in a reticulose surface and a sharp, angular border.

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