Cyclostomaria praemonarii, 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 : 26-28

Cyclostomaria praemonarii n. sp.

( Figs 37–40 )

Type specimen – GBA 2017/001/0001.

Type locality – Hierlatz Alpe , Hallstatt ( Austria).

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

Derivation of name – Referring to the stratigraphically younger [Davoei to Margaritatus Zone (Pliensbachian), Lower Jurassic] C. monarii .

Diagnosis – Low spired shell, consisting of whorls with rounded cross-section, two angles at spire and umbilical suture lines, respectively. Top of convexity on whorls in higher position than suture, convex ramp connecting them. Suture running at periphery of former whorl. Base low with convex wall and broad umbilicus. Selenizone between two cords, concave, rather wide and placed at outer face little below top line of whorl. Subregularly repeating, collabral riblets on ramp, crossed by single cord along top of whorl; nodules at intersections. Dense spiral threads between selenizone and periphery; base seemingly smooth. Selenizone without lunulae and spiral ornament.

Material – A worn, shelly whorl-fragment, surrounding also cross-section of two previous whorls.

Dimensions – Height of preserved whorl: 9.5 mm, width: 21.5 mm.

Description – The remnants indicate a low, almost planispiral shell that has axially round whorl cross-sections; scar of the broken former whorls shows presence of a rather wide umbilicus. A concave selenizone runs well above the midwhorl but somewhat below the most adapical line of the whorl; the belt between the selenizone and the impressed (upper) suture is rather wide and mostly convex but a narrow concave band accompanies the suture. The suture follows the periphery of the former whorl.

The ornament is poorly preserved but the coarser elements are observable. Subregularly repeated, unequally strong riblets are visible in the belt between the selenizone and the adapical suture. Their shape is almost straight in slightly prosocline orientation with a short prosocyrt part along the selenizone. Weaker riblets or thick growth lines seem to be developed also on the outer whorl face occasionally. Two cords, the strongest spiral ornamental elements, limit the selenizone. At the first third of the distance toward the adapical suture from the selenizone, single marked spiral thread is visible and two weak threads are also present between the aforesaid one and the cord along the selenizone. Between the strongest spiral thread on the ramp and the selenizone, the collabral riblets weaken; nodules are at crossings with the riblets. The outer face is covered by dense spiral threads of unequal strength, crossed only by strongly prosocyrt growth-lines, which are visible only in few spots. No lunulae are observable in the selenizone; the probably delicate growth-lines are not observable on the available specimen. Preserved parts of the outermost base zone are smooth.

Remarks – The available shelly fragment well agrees with the penultimate whorl of the type specimens of Cyclostomaria monarii in its dimensions and shape. However, the almost full absence of the spiral ornament on the adapical part of the whorl means a significant difference that distinguish this specimen from C. monarii , which has a dense, subregular network ornament adapically and abapically from the selenizone at corresponding shell size.

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

Figures

Figs 37–40. Holotype of Cyclostomaria praemonarii n. sp. from the Sinemurian to lowermost Pliensbachian interval (Lower Jurassic) of the Hierlatz Limestone in the Hierlatz Alpe, Hallstatt, Austria, GBA 2017/001/0001.– 37–38. Magnified apical and lateral views, ×2. – 39–40. The same views without magnification