Biconomphalus singularis, 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 : 63-64

Biconomphalus singularis n. sp.

( Figs 5–9 )

Type specimen – Holotype: GBA 2019/009/0001 . 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 – Singularis (Latin) = single, referring to the only known specimen and species in the genus.

Diagnosis – Same as for the genus.

Material – The holotype only.

Measurements – Holotype, D = 8.1 mm.

Description – The available shell has a moderately high, conoidal spire with blunt apex and a lower basal conoid. All whorls, having almost flat but convex surface, are edged by feebly impressed, almost flush suture. The periphery is sharply angular. Wall of the base is convex a little on the earlier whorls then changing into feebly concave in the latest growth phase that means about the last half coil. Deepest part of this concavity is observable along the periphery and this narrow belt is concave also on the earlier base parts. The umbilicus is moderately broad with a sharply angular rim. In cross-section, the whorls are quadrangular; the aperture and the peristome must be similarly shaped but no parts of theirs are preserved; in lack of any parietal encrustation, the peristome appears to be discontinuous there.

The earliest teleoconch whorl bears the sparse, suture to suture eucycloidean riblets that are substituted on the subsequent whorls by denser and thinner collabral threads, extending usually from suture to suture but some shorter ones, which do not reach the upper suture, also occur. These threads are crossed by very thin or obscure spiral lines on the whorls. Stronger, dense spiral lines give the main ornament of the base but a few marked threads also occur along the periphery and around the umbilicus. The growth lines are prosocline on the whorls and opisthocyrt on the base.

Remarks – The shape of Biconomphalus singularis n. sp. is similar to that of the type species of Callotrochus Kutassy in Wenz, 1938 but this latter one does not have any trace of eucycloidean (early) ornament. Eucyclomphalus hierlatzensis specimens in early growth stages may show similar appearance because of their ornament, composed of also fine collabral threads on the whorls. However, the differences mentioned in the genus distinction are recognisable also on these shell parts although in less marked form.

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

Figures

Figs 1–19. Species of Eucycloidea. – Figs 1–4. Eucyclompalus? subgradatus n. sp., holotype (GBA 2019/009/0004). – 1–3. Apertural, basal and lateral views, ×2. – 4. Details of the ornament, ×8. – Figs 5–9. Biconomphalus singularis n. gen. n. sp., holotype (GBA 2019/009/0001). – 5–7. Apertural, basal, and lateral views, ×3. – 8–9. Details of the ornament on spire and base, ×6. – Figs 10–14. Riselloidea noszkyi Szabó, 1995 (GBA 2019/009/0002). – 10–12. Apertural, basal, and dorsal views, ×2.5. – 13. Details of the ornament, ×5. – 14. Fragment of another shell with denser collabral ornament (GBA 2019/009/0003), ×2.5. – Figs 15–19. Cupaniella praebiplicata n. sp. – 15. Holotype (GBA 2019/009/0005), s = suture, f = outer groove of the inner fold, ×8. – 16–17. Young specimens, paratypes (GBA 2019/009/0006–7), arrow indicates furrow, the early phase of formation of inner (palatal) plica of last whorl, ×6. – 18. Paratype (GBA 2019/009/0008), an inner mould with traces of the inner fold within penultimate and last whorl, and reflection of latest peristome, ×6. – 19. A fragmentary and partly embedded, full grown specimen, paratype (GBA 2019/009/0009), letters mean the same as for Figure 15, ×6