Arionoceratidae Dzik, 1984

Kröger, Björn, 2004, Revision of Middle Ordovician orthoceratacean nautiloids from Baltoscandia, Acta Palaeontologica Polonica 49 (1), pp. 57-74 : 72

Family Arionoceratidae Dzik, 1984 , emend. Gnoli (1998)

Diagnosis.— Orthoceratidae with a relative short straight to slightly cyrtoconic (most commonly endogastric) shell. The cross section of the shell is circular. The narrow cylindrical siphuncle is central with “suborthochoanitic, terminally very acuminate, and short septal necks” ( Gnoli 1998). The connecting rings slightly expanding within chambers. A big protoconch usually more than 2mm in length, ogive−like in shape is crossed by a long caecum linked apicad to the beginning of the conch by a short prosiphon (see Gnoli 1998).

Remarks.—The family is common in the Ludlow of Bohemia, e.g., Arionoceras arion (Barrande) and the Wenlock of Sardinia, e.g., Arionoceras submiliforme (Meneghini) . The earliest representative known so far is Arionoceras gyratum (Miagkowa) from the Llandovery of Siberia ( Miagkowa 1967). Arionoceras lotskirkense sp. nov., described herein, is of Middle Ordovician age.