XXIX.—An EarlyDictyoconus, and the GenusOrbitolina: Their Contemporaneity, Structural Distinction, and Respective Natural Allies

Abstract

The author summarises recent reports regarding the appearance in Mesozoic rocks of Blanckenhorn's genus Dictyoconus, long supposed to have originated in the Middle Eocene. He figures and describes the best known of these Mesozoic forms, in order to place its age and generic attribution beyond question, and discusses the problem of its relationship to allied genera as affected by its early appearance. He then describes d'Orbigny's contemporary (Cretaceous) genus Orbitolina, with which Dictyoconus has often been confused, in order to show its radical difference in structure and the characteristics of forms which can be more justly regarded as related to it. He also discusses the genotype of Orbitolina, since the species lately quoted as such is unsuitable.

The type species of the genus <i>Orbitolina</i> D’Orbigny, 1850 (Foraminifera)

“…If one accepts this situation, then the numerous species regarded as belonging to Orbitolina would have to be assigned to a new genus. Therefore we recommend the suppression of Orbitolina gigantea as type species and the recognition of Orbitolina concava as replacement type species of Orbitolina, as originally suggested by Davies (1939). This will negate the need for a major revision of orbitolinid taxonomy and allow the genus Palorbitolina to remain valid.…”

Dictyoconus aydimi (Gallardo-Garcia and Serra-Kiel, 2016) comb. nov., larger benthic foraminifera from the Middle-Upper Eocene of the Middle East (SE Turkey, Iraq, SW Iran, Oman): New evidence for Arabian Plate faunal provincialism

“…indicus Davies display a rather complex network consisting of several series of both rafters and intercalary beams (Davies, 1939;Henson, 1948;Hottinger and Drobne, 1980;Hottinger, 2007; Gallardo-Garcia and Serra-Kiel in Serra-Kiel et al, 2016) ( Figure 4C).…”

“…In our opinion, the deuteroconch is not well discernible in the holotype specimen and the occurrence of several "beams" followed by the neanic chambers with just one rafter and one intercalary beam would be a curious feature. In any case, the presence of skeletal elements in the deuteroconch of Dictyoconus, although debatable with respect to suprageneric classification (Orbitolininae vs. Dictyoconinae), is accepted as species criterion (D. indicus with and D. aegyptiensis without skeletal elements; Davies, 1939;Hottinger and Drobne, 1980;Hottinger, 2007; Gallardo-Garcia and Serra-Kiel in Serra-Kiel et al, 2016). Again, such a feature is not an adequate criterion for the separation of Rogerella from Dictyoconus.…”

“…The moderate simple/complex subepidermal network of Rogerella is considered as nothing but a specific feature. Other species of Dictyoconus, such D. aegyptiensis (Chapman) or D. indicus Davies, display a rather complex network, consisting of several series of both rafters and intercalary beams (Davies, 1939;Henson, 1948;Hottinger and Drobne, 1980;Hottinger, 2007;Serra-Kiel et al, 2016) (Figure 4C).…”

Agglutinated Conical Foraminifera (Orbitolinidae, Coskinolinidae) From the Upper Cretaceous (Campanian) of Greece, With Description of Paracoskinolina Klokovaensis N. Sp.

“…The new species has been described and illustrated by Fleury (1970) as Dictyoconus sp. Contrasting with Paracoskinolina Moullade, Dictyoconus Blanckenhorn has pillars in the central zone that alternate in position between subsequent chambers (e.g., Davies, 1930Davies, , 1939Arnaud-Vanneau, 1980;Loeblich and Tappan, 1987). Having a single rafter in the chamber marginal zone, P. klokovaensis can be compared with P. arcuata Arnaud-Vanneau, 1976 andP.…”