Pleurotomaria? laponya, Szabó, 2017

Szabó, János, 2017, Gastropods of the Lower Jurassic Hierlatz Limestone Formation, part 3. New pleurotomarioideans from the fauna of Hierlatz Alpe (Hallstatt, Austria), Fragmenta Palaeontologica Hungarica 34, pp. 9-48 : 32-35

Pleurotomaria? laponya n. sp.

( Figs 110–115 )

Type specimen – Holotype: GBA 2018/002/0010.

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 – Laponya (Hungarian) = a synonym for “flat” or “depressed”.

Diagnosis – Depressed shell with spire of subglobular outline. Whorls having obscure angulation between flattish outer face and strongly convex “ramp”, sloping both adaxially and abaxially. Suture deeply impressed and running along peripheral angulation of former whorl. Last whorl having high outer face, being rounded angular at rim of base, providing also periphery. Base flattish convex as whole and having convex wall and broad umbilicus. Single spiral thread indicating roughly abaxial edge of ramp and limiting strong, wide and flat collabral ribs, starting at suture. Further spiral threads between ramp and rim of base; two of them limiting selenizone, running at rim of ramp. Exposed abaxial parts of base smooth. Growth lines slightly prosocline and prosocyrt on ramp and prosocline-prosocyrt on outer face, opisthocyrt on abaxial belt of base.

Material – Single specimen without peristomal and earliest shell parts. The base is visible only in small abaxial parts.

Measurements – Maximal visible diameter: 31.5 mm.

Description – The shell is depressed with subglobular or perhaps cyrtoconoidal outline of the spire. On the spiral side, the whorls have an obscure, widely rounded angulation between the flattish-convex outer face and the strongly convex “ramp” that slopes both adaxially and abaxially. So, the suture appears deeply impressed; its position is below the angulation of the previous whorl somewhat abaxially from the selenizone. The selenizone itself is placed just below the angulation of the whorls; its adapical edge seems to coincide with the angulation. The width of the selenizone is above 20% of the whorl height, suture to suture distance, on the penultimate whorl. On the last whorl a rather wide outer face is observable with a clear but rounded angulation at the rim of the base that corresponds also to the periphery. The base as a whole is flattish convex with a convex wall, and a broad umbilicus as it is suggested by the scar of the earliest shell part.

The ramp is sculptured by marked, wide, regularly repeated collabral costae and thin growth threads between the suture and a spiral thread, running near the angulation and the adaxial edge of the selenizone. The costae are sparsely distributed but the growth threads are dense and equally cover the costae and their interspaces, too. The early costae are sharp but they become wider, flat undulations towards the peristome. The costae gradually widen from the suture abaxially then rather suddenly terminate at the aforementioned spiral thread. Between this boundary thread and the edge of the selenizone, a narrow flat-concave belt can be found with another spiral thread and undulations, caused by the ends of the costae. Two spiral threads border the selenizone that is smooth on the whorls, on which it is preserved. Further spiral threads are between the selenizone and the rim of the base. On the peripheral angulation, a spiral cord is observable just above the suture that vanishes for the latest whorl ( Fig. 114 ). The visible abaxial parts of the base are smooth. The growth lines are slightly prosocline and prosocyrt on the ramp and prosocline-prosocyrt on the outer face, opisthocyrt on the abaxial belt of the base.

Remarks – The ribs of the ramp and the track of the selenizone are reflected on the inner mould as undulation. Between the trace of the selenizone and the periphery, the outer face of the inner mould is feebly concave.

Pleurotomaria ? laponya n. sp. is similar to the depressed “varieties” of P. debuchii J. A. Eudes-Deslongchamps, 1849 . Actually the taxonomical status of this “mega-species” has not yet been arranged satisfactorily (see also MONARI & GATTO 2013, p. 771). The situation is similar to the case of “ Pleurotomaria foveolata ” ( SZABÓ 2017) : is Pleurotomaria debuchi a single species or a group of unsatisfactorily known species, and does this/these species belong to Pleurotomaria at all? In the Hierlatz Alpe fauna, some “varieties” of P. debuchi occur ( STOLICZKA 1861, SZABÓ 2008, 2009) but all are different from P.? laponya n. sp. The most similar ones are those forms, which have been identified by STOLICZKA (1861) as P. suessi (see SZABÓ 2008); however, though they have similar shape, their ornament is strongly different since they have dense and marked spiral threads on the ramp, and their denser riblets are almost as thin as the spiral threads; they lack the dense growth threads that are present on the ramp of P.? laponya n. sp. The question mark after the genus name indicates the opinion of the writer that application of “ Pleurotomaria ” may be not right for this and the similar species.

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

Figures

Figs 110–115. Pleurotomaria? laponya n. sp., holotype (GBA 2018/002/0010). – 110–111. Apical view (×2 and ×1). – 112–113. Lateral view (×2 and ×1). – 114. Oblique lateral view to make the cord along the peripheral angulation of the penultimate whorl visible (×2). – 115. Details of the ornament and selenizone (×5, cut from Fig. 114)