Foveolaria bicarinata, Szabó, 2016

Szabó, János, 2016, Gastropods of the Lower Jurassic Hierlatz Limestone Formation, part 2. Some new archaic type slit-bearing components from the fauna of the Hierlatz Alpe (Hallstatt, Austria) and the Bakony Mts (Hungary), Fragmenta Palaeontologica Hungarica 33, pp. 3-30 : 16-17

Foveolaria bicarinata n. sp.

( Figs 15–18 )

Type specimen – GBA 2017/001/0003.

Type locality – Hierlatz Alpe , Hallstatt ( Austria).

Type strata – Within Sinemurian to lowermost Pliensbachian (Lower Jurassic) Hierlatz Limestone .

Derivation of name – Bicarinata (Lat.) = having two ridges; referring to the sharp spiral angulations, limiting the concave outer face of the whorls.

Material – Single fragmentary specimen with remnants of three whorls that are characteristic enough to outline a new species.

Dimensions – Width: 12.2 mm.

Diagnosis – Gradate, medium high shell of whorls with rather steep ramp and concave outer face with sharply angular edges, abapical one providing periphery. Base low, subglobose as whole with moderately convex wall; phaneromphalous, umbilical rim rounded angular. Suture rather deeply impressed, running somewhat adaxially from periphery of former whorl. Ramp ornamented by regularly repeating collabral riblets; outer face with single thin thread above midline and some obscure striae above it. Below peripheral sharpness, another but weaker keel visible, remaining parts of base covered by quirinii type spiral ridges. Selenizone bearing lunulae on earlier whorls, gradually vanishing on last whorl.

Description – A gradate, medium high shell is available; its reconstructed height is about 20 mm. The whorls have rather steep ramp that is slightly convex on the earlier whorls but flat on the last whorl. At its abapical edge, the spiral angulation is marked, sharp keel-like on the last whorl but less prominent, slightly rounded on the earlier shell parts. A strong spiral thread gives the adapical boundary for the selenizone that is concave. The outer face is markedly concave with an abapical edge that is also sharply angular. This ridge corresponds to the periphery. The base is low, subglobose as a whole and has moderately convex wall; it is rather broadly phaneromphalous and has a rounded angular umbilical rim. Near the peripheral angulation, a weaker keel also develops on the base; the suture is seamed about halfway between these two keels, so the suture is rather deeply impressed.

Regularly repeating collabral riblets ornament the ramp, they start at the adapical suture, and with gradual weakening, terminate at the rim of the selenizone. On the ramp, no spiral ornament is observable on the preserved shell fragment. The outer face bears a single thin thread above the midline and some obscure striae are also visible above it. Between the weak keel of the base at the peripheral belt and the umbilicus, quirinii type spiral ridges represent the ornament. They are denser in the abaxial half than in the remaining part of the base. The selenizone bears lunulae on the earlier whorls that gradually vanish on the last whorl. The growth lines are strongly prosocline on the ramp with markedly prosocyrt subsutural and feebly prosocyrt remaining parts; on the outer face, the growth lines are feebly prosocline and clearly prosocyrt. The growth lines of the base are more prosocline (~45°) than it is common in Foveolaria (~30°), and they are somewhat more opisthocyrt than it is usual.

Remarks – Foveolaria bicarinata n. sp. resembles F. suemegensis n. sp. (see below) in the keel like angulations on the whorl surface and at the periphery, limiting a markedly concave outer face. The latter species has higher, somewhat acute spire, much widely developed and steeper ramp. Moreover, F. suemegensis has only barely developed or obscure spiral ornament on the latest whorls, while F. bicarinata bears few but clear spiral threads and sharp collabral riblets. Their dimensions are also significantly different.

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

Figures

Figs 15–29. New species of Foveolaria n. gen. from the Sinemurian to lowermost Pliensbachian interval (Lower Jurassic) of the Hierlatz Limestone in the Hierlatz Alpe, Hallstatt, Austria. – 15–18. Holotype of Foveolaria bicarinata n. sp., GBA 2017/001/0003, all ×3.8. – 15. Dorsal view. – 16. Apical view. – 17. Basal view. – 18. Peristomal view. – 19–22. Holotype of Foveolaria conoidea n. sp., GBA 2017/001/0004, all ×4. – 19. Dorsal view. – 20. Apical view. – 21. Basal view. – 22. Peristomal view.– 23–26. Holotype of Foveolaria globosa n. sp., GBA 2017/001/0005, all ×4. – 23. Dorsal view. – 24. Apical view. – 25. Basal view. – 26. Peristomal view. – 27–29. Foveolaria sp., GBA 2017/001/0006, all ×4. – 27. Apertural view. – 28. Basal view. – 29. Dorsal view