Biconomphalus, Szabó, 2018

Szabó, János, 2018, Gastropods of the Lower Jurassic Hierlatz Limestone Formation, part 4. New eucycloidean, trochoidean, neritimorph, and caenogastropod taxa in the fauna of the Hierlatz Alpe (Hallstatt, Austria), Fragmenta Palaeontologica Hungarica 35, pp. 61-84 : 62-63

Biconomphalus n. gen.

Type species – Biconomphalus singularis n. sp.

Derivation of name – Name refers to the biconoidal shell shape and the associated umbilicus.

Diagnosis – Biconoidal, thin walled shell with low whorls of quadrangular cross-section. Whorl surface convex but almost flat, suture following former periphery in shallow depression. Periphery simply angular on early shell but becoming keel-like on last whorl. Base wall feebly convex then changing into somewhat concave on latest half whorl. Moderately broad umbilicus, having sharply angular rim. Peristome discontinuous at parietal region. Ornament of sparse, prosoclineprosocyrt riblets on initial teleoconch, dense, prosocline-straight threads subsequently; all collabral. Basal growth lines opisthocyrt. Obscure spiral lines on whorls; various, dense spiral threads on base.

Remarks – The shell of Biconomphalus n. gen. resembles that of Eucyclomphalus von Ammon, 1892 . The two genera most prominently differ in the form of the base; while this shell part is almost flat walled in Biconomphalus n. gen., so the entire base well approaches the shape of a cone, Eucyclomphalus has subglobular base with strongly convex wall. Another difference is in the formation of the suture that is almost flush on the whole shell of Biconomphalus n. gen. but impressed below the periphery in Eucyclomphalus so causing a subpagodiform outline. The late teleoconch of Sertomphalus Gründel, 2007 shows the same differences as Eucyclomphalus from Biconomphalus n. gen. They differ also in the earliest growth phases; the early teleoconch of Sertomphalus is markedly coeloconoidal, Biconomphalus n. gen. has simple cone outline. This shell part is poorly known in the type species of Eucyclomphalus .

The short diagnosis from GRÜNDEL (2007) permits to place Biconomphalus n. gen. into Eucyclidae ; however, it is an extreme form amongst the other genera, which have more or less pagodiform shell and rather subglobose base with more convex wall. That is why the attribution of Biconomphalus n. gen. to Eucyclidae must be regarded as uncertain.