Orthoceratida, Kuhn, 1940

Aubrechtová, Martina, Turek, Vojtěch & Zicha, Ondřej, 2020, Early ontogenetic growth stages of Middle Ordovician orthoceratoid cephalopods from Bohemia, Acta Palaeontologica Polonica 65 (3), pp. 575-588 : 585

Orthoceratida indet. sp. 5

Fig. 6C .

Material.— One specimen (NM L 59872), embryonic shell, from the locality Malé Přílepy(50.0124397 N, 14.1148514 E); Dobrotivá Formation , upper Darriwilian Stage, Middle Ordovician; Czech Republic .

Description. —The specimen is a counterpart of an embryonic shell. Total length is 3.3 mm. Shell diameter is 1.8 mm along the specimen length; no marked constriction is discernible on the phragmocone. The phragmocone is circular in cross-section. The external shell surface at its apical part shows fine longitudinal structures, while in the adoral part, transverse lirae are observed.

Remarks. —The size and shape of the initial chamber in NM L 59872 is very similar to that in MWB S 06827 assigned above to Orthoceratida indet. sp. 4. The preservation of both specimens is, however, too fragmentary to allow more precise comparisons and unequivocal taxonomic classification.

Figures

Fig. 6. Apical and juvenile shell parts of orthoceratid cephalopods; Middle Ordovician, Darriwilian Stage, Šárka and Dobrotivá formations, Czech Republic. A. Bactroceras sandbergeri (Barrande, 1867), MWB S 06823, Volduchy, third phragmocone chamber (estimated based on shell diameter) and adjacent part of body chamber. B. Orthoceratida indet. sp. 4, MWB S 06827, Volduchy, counterpart of initial chamber and adjacent part of phragmocone and one corroded phragmocone septum; note longitudinal striae. C. Orthoceratida indet sp. 5, NM L 59872, Malé Přílepy, counterpart (C1), latext cast C2); note longitudinal striae.