Neorotomaria, Szabó, 2017

Genus Neorotomaria View in CoL n. gen.

Type species – Neorotomaria obertraunensis n. sp.

Derivation of name – A modification from Pleurotomaria ; νΈΟς (neos, Greek) = new.

Diagnosis – Conoidal shell consisting of rather high number of low whorls, and flat to concave base with angular contact to the whorl surface. Suture impressed. Whorls convex as whole but having concave spiral belts. Angulation with narrow ramp occurring on latest whorls or never. Selenizone at or below midwhorl. Early teleoconch selenizone bearing midline thread, corrugated by coarse lunulae then changing into smooth carina. Ornament of regularly repeating, sharp riblets and spiral threads with granules at crossings on early teleoconch. Spiral threads, cords and carinae with or without nodules and tubercles ornamenting all later teleoconch whorls and base, crossed by thin, subregularly repeated growth threads and lines.

Description – The earliest shell parts, the protoconch and one or two teleoconch whorls, are unknown in both species, ascribed to Neorotomaria . The first preserved teleoconch whorls are more convex than the succeeding ones, which become flattened and may have even feebly concave belts above and/or below the selenizone. The submedian cord/carina of the selenizone is one of the most prominent morphological elements on the whorl surface. No true spiral angulation develops on the early teleoconch whorls between the sutures but the transition of the whorl surface towards the base is angular just like on the latest whorls. The suture is moderately impressed. The base is flat or concave as a whole with feebly convex or flat wall, and has a rather broad umbilicus. No peristome part is known. Width of the selenizone is quite high, 15–18% of the distance between two neighbouring sutures; their position is at or just little below the midwhorl. The periphery of the whorls usually coincides with the abaxial rim of the base; sometimes the cord/ carina of the selenizone seems to be the farthest line from the axis.

The earliest known whorls have a network ornament. From the network, the transverse elements, which are collabral riblets, gradually vanish or weaken but the spiral components are present also along the next shell parts, and a few new ones also appear. Beside them, granules or granule-like, marked lunulae ornament the submedian thread of the early selenizone that becomes a smooth cord, then carina on the succeeding whorls. Granules appear also in the intersections of the network ornament and along some other spiral threads. In the subsutural belt, nodules develop from the granules at crossings with a stronger spiral cord, usually they are collabrally elongated and fading out toward the selenizone. This row of nodules corresponds to the adapical series of nodes in Pleurotomaria ; they will strengthen as low angulation of the latest whorls in Neorotomaria subgradata n. sp. In later growth stages new types of riblets, granules and nodules also appear mainly above the rim of the base. The growth lines may appear occasionally also as fine riblets. Sparse spiral cords and threads or ribbons ornament the base. The growth lines are of pleurotomariid type on the whorls, i.e. they approach the rims of the selenizone asymptotically and meet it under low angle. Their shape is strongly prosocyrt and prosocline above and strongly prosocyrt but opisthocline below the selenizone, respectively. Together, they indicate a just slightly prosocline outer lip and a moderately deep sinus. The growth lines of the base are feebly prosocline and opisthocyrt.

Remarks – In both Neorotomaria species, the earliest preserved parts are about the 3rd or 4th teleoconch whorls, yet having no angulation. In this growth stage, Pleurotomaria Defrance, 1826 species already have clearly angular whorl surface ( MONARI & GATTO 2013, p. 754; see also Figs 23, 25, 28 View Figs 14–28 , 45 View Figs 29–46 here). In Neorotomaria , angulation does not develop at all in N. obertraunensis n. sp. but it is lacking only from the earliest whorls in N. subgradata n. sp., then an obscure angulation gradually develops. Since the monotype of the type species is not a full grown specimen, there is a possibility that angulation develops similarly to N. subgradata but only in the latest growth phase. Therefore, the long early lack of angulation means the major difference from Pleurotomaria .

In the coarse nature of the early lunulae, the early teleoconch whorls of Neorotomaria n. gen. shows some similarity to Granulizona n. gen. (see below), however, the details of the ornaments are different. Riblets in Granulizona are sparse, wide, actually transverse undulations, crossed by dense, thin spiral threads that form a pattern, different from the sparse network of sharp riblets and similarly strong spiral threads in Neorotomaria . The subsequent whorls become more convex with rather deeply impressed suture in both genera, however, Granulizona has exclusively spiral ornament on this shell part.

Distribution – Sinemurian to Pliensbachian (Lower Jurassic) of the Hierlatz Alpe (Hallstatt, Austria).