Callotrochus? avernoides, 1938

Callotrochus? avernoides View in CoL n. sp.

( Figs 20–25 View Figs 20–50 )

Type specimens – Holotype: HNHM, M 59.157; paratype: HNHM, M 57.3617. Type locality – Hierlatz Alpe (Hallstatt, Austria).

Type strata – Lower Jurassic Hierlatz Limestone from the Semicostatum Zone (Lower Sinemurian) to Jamesoni Zone (Lower Pliensbachian) interval.

Derivation of name – Referring to the similarity to Proconulus avernus (Stoliczka, 1861) .

Diagnosis – Proconuliform thin walled shell with barely convex to flat whorls and flush suture. Subconoidal base with shallow concavity around narrow umbilicus. Whorls and base with weak, evenly spaced spiral lineation.

Material – Two fragmentary specimens from the collections of R. Streda. The specimens have been registered as “ Trochus epulus d’Orb. ” in the collection of the HNHM.

Measurements – Holotype HNHM, M 59.157, W = 10.1 mm, H = 14.7 mm; paratype, W = 10.9 mm, H = 14.7 mm.

Description – Shells are thin walled, biconoidal and their shape closely approaches the form of the typical Proconulus species. It means a conoidal spire with feebly convex whorls that are separated by almost flush suture. Last whorl turns through a rounded-angular periphery into a subconoidal base, having feebly convex wall that changes into slightly concave around the abapical part of the umbilical lip that encloses a narrow umbilicus. The whorl cross-section is quadrangular; its abapical-abaxial angle is strongly rounded; meeting of the umbilical and the basal lip is slightly rounded angular in nearly 90°.

Dense, rather weak spiral threads of slightly variable thickness give the ornament of the whorls; similarly wide, shallow furrows separate them. Poorly preserved remnants show that the base is probably covered by similar ornament. The growth lines are delicate, slightly prosocline and straight.

Remarks – Both specimens lack the earliest and the latest shell parts. The apparent bases and umbilical lips show slight, smooth enamel that permits to assume simple, thin actual inner lip. The poor preservation precludes a safe identification on the genus level. However, the preserved parts do not exclude that this species belongs to Callotrochus , excepting the fact that the only formerly known species in this genus does not have clear spiral ornament.

The similarity to the monotype of “ Trochus avernus Stoliczka ” is rather high but the presence of an umbilicus in Callotrochus ? avernoides n. sp. clearly distinguishes the available specimens since Stoliczka’s species is anomphalous and its preserved inner lip is of Proconulus type. Besides, P. avernus has a deeply impressed suture while it is flush in Callotrochus ? avernoides n. sp.

Occurrence – Within Sinemurian to lowermost Pliensbachian (Lower Jurassic) part of the Hierlatz Limestone Formation in Hierlatz Alpe, Hallstatt, Austria.