Michelinoceratinae Flower, 1945 emend. Sweet (1964)

Kröger, Björn, 2004, Revision of Middle Ordovician orthoceratacean nautiloids from Baltoscandia, Acta Palaeontologica Polonica 49 (1), pp. 57-74 : 63

Subfamily Michelinoceratinae Flower, 1945 emend. Sweet (1964) , emend. Ristedt (1968)

Diagnosis.— Orthoceratidae with a smooth or transversely striated shell, sometimes forming rings. The septal necks are ortho− to suborthochoanitic. Endosiphuncular deposits are not developed. Between the initial chamber and the rest of the conch no constriction is developed.

Remarks.— More than twenty genera are assigned to the Michelinoceratinae , but for the most part the shape of their apical parts is unknown. Therefore, it is not clear if these genera belong to the Michelinoceratinae sensu Ristedt (1968) . Many authors refer to the definition of Sweet (1964), which

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0 0 0.02 0.04 0.06 0.08 0.10 0.12 0.14 e describes the Michelinoceratinae not by the shape of the initial chamber but by the absence of endosiphuncular deposits. But, as can be shown in the case of the Orthoceratidae , the endosiphuncular deposits may be strongly depressed and occur only in the very apical parts of the phragmocone. The apex of the conch in these cases is crucial for defining of the taxon at a (sub−) family level, too. Therefore, the Michelinoceratinae are mostly regarded as a taxonomical wastebasket for all Orthoceridae with a more or less smooth sculpture, without any known siphuncular deposits and without known apical parts.