Hinlopoceras Kröger & Pohle 2021, gen. nov.

Genus Hinlopoceras gen. nov.

urn:lsid:zoobank.org:act: 1B85F4BE-F04C-4D03-A909-29003ACF507B

Hinlopoceras tempestatis gen. et sp. nov. from Olenidsletta Member, V1a trilobite zone, Blackhillsian, Floian.

Longicones with slightly curved endogastric curvature during early ontogeny and orthoconic growth during later ontogeny, with cross section changing from circular in juvenile to compressed in adult growth stages; angle of expansion decreases during growth from ca 14° to 10°; ornamented with distinct transverse growth lines and striae; weak transverse annuli occur during latest growth stages; approximately four chambers occur at a distance similar to the corresponding conch height; siphuncle narrow with diameter ca ⅛ of corresponding conch height, strictly marginally positioned, with slightly concave segments and loxochoanitic septal necks.

Referring to Hinlopen Strait, Svalbard, the type region of this genus.

The new genus is unique within the Rioceratidae in having a combination of a relatively large angle of expansion, wide septal spacing, and a distinct transversely lirate ornamentation. The internal characters of this genus are relatively poorly known, because most specimens available have a strongly recrystallized phragmocone. The thin marginal siphuncle is nearly tubular or only very slightly concave, which can best be compared with that of Svalbardoceras gen. nov. The consistently poor preservation of the internal shell of specimens of Hinlopoceras gen. nov. in beds where internal features of Svalbardoceras gen. nov. are better preserved indicates that the septa were originally more fragile and sensitive to early dissolution and/or implosion. Species of Hinlopoceras gen. nov. can be distinguished from species of Svalbardoceras gen. nov. by their distinct ornamentation; in Hinlopoceras gen. nov. the conch is ornamented with transverse bands or striae, in Svalbardoceras gen. nov. the ornament consists of fine irregularly spaced growth lines.