Weyerella molaris (Vöhringer, 1960)

Figs 8B, 10D, 91–93; Tables 89–90

Gattendorfia molaris Vöhringer, 1960: 158, pl. 5 fig. 1, text-fig. 33.

Gattendorfia molaris – Weyer 1976: 845, text-fig. 5. — Korn 1994: 74, text-figs 65e–g, 66i–j, 67e, 68d.

— Korn & Weyer 2003: 96, pl. 1 figs 13–14, pl. 2 figs 18–19. — Sprey 2002: 53, text-fig. 18d. Weyerella molaris – Korn 2006: text-fig. 3h.

non Gattendorfia molaris – Ruan 1981: 83, pl. 20 figs 1–26. — Sheng 1989: 116, pl. 34 figs 3–5.

Diagnosis

Species of Weyerella with a conch reaching 30 mm diameter. Conch at 15 mm dm thickly discoidal, subevolute (ww/dm ~0.50; uw/dm ~0.40). Whorl profile at 15 mm dm weakly depressed (ww/wh ~1.35); coiling rate low (WER ~1.70). Venter rounded, umbilical margin narrowly rounded. Growth lines fine, wide-standing, with convex course. With moderately deep constrictions on the shell surface; with moderately coarse internal shell thickenings. Suture line with narrowly lanceolate external lobe and lanceolate adventive lobe.

Material examined

Holotype

GERMANY • Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3c; Vöhringer Coll.; illustrated by Vöhringer (1960: pl. 5 fig. 1) and Korn (1994: text-fig. 65e); re-illustrated here in Fig. 91A; GPIT-PV-63930.

Paratypes

GERMANY • 6 specimens; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 2; Vöhringer Coll.; GPIT-PV-63928–GPIT-PV-63929, GPIT-PV-63931, GPIT- PV-63960–GPIT-PV-63961, GPIT-PV-64003 .

Additional material

GERMANY • 1 specimen; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone; Schmidt 1921 Coll.; BGR X4643 • 1 specimen; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone; Schindewolf 1925 Coll.; MB.C.4687 • 3 specimens; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 1; Vöhringer Coll.; MB.C.31178.1–3 • 2 specimens; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 2; Vöhringer Coll.; MB.C.31179.1–2 • 2 specimens; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3b; Vöhringer Coll.; MB.C.31180.1–2 • 2 specimens; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3c; Vöhringer Coll.;MB.C.31181.1–2 • 3specimens; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3d; Vöhringer Coll.; MB.C.31182.1–3 • 2 specimens; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3e; Vöhringer Coll.; MB.C.31183.1–2 • 1 specimen; Rhenish Mountains, Oberrödinghausen, west of railway cutting; Hangenberg Limestone, loose material; Korn 1977 Coll.; MB.C.31184 • 1 specimen; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 2; Weyer 1993–1994 Coll.; MB.C.31185 • 2 specimens; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3a; Weyer 1993– 1994 Coll.; MB.C.31186.1–2 • 2 specimens; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3b; Weyer 1993–1994 Coll.; MB.C.31187.1–2 • 23 specimens; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3d1; Weyer 1993–1994 Coll.; MB.C.31188.1–23 • 41 specimens; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3d1b; Weyer 1993–1994 Coll.; MB.C.31189.1–41 • 13 specimens; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3d2; Weyer 1993–1994 Coll.; MB.C.31190.1–13 • 15 specimens; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3e; Weyer 1993–1994 Coll.; MB.C.31191.1–15 • 9 specimens; Rhenish Mountains, Hasselbachtal; Hangenberg Limestone, bed 57; Weyer 1993–1994 Coll.; MB.C.5240.8, MB.C.5240.21–28 • 1 specimen; Rhenish Mountains, Oese, old quarry; Hangenberg Limestone, bed 28; Weyer & Korn 2000 Coll.; MB.C.5260.2 • 1 specimen; Rhenish Mountains, Oese, old quarry; bed interval V; Paproth Coll.; MB.C.5284 .

Description

Holotype GPIT-PV-63930 is a fairly well-preserved specimen almost completely covered with shell material; it has a conch diameter of almost 20 mm (Fig. 91A). It is thinly discoidal and subinvolute (ww/ dm = 0.40; uw/dm = 0.29) with a low coiling rate (WER = 1.70). The whorl profile is almost circular. It can be clearly seen that during the last whorl there is increasing overlap upon the preceding whorl; therefore, the uw/dm ratio decreases considerably within a short growth interval. The ornament consists of fine growth lines, with a convex arch on the flank and extend in backward direction, to form a deep ventral sinus (Fig. 93I). In addition, very weak constrictions can be seen on the shell surface; they are restricted to the middle of the flank.

Paratype GPIT-PV-63928 (Fig. 91B) has almost the same size (19 mm conch diameter), but differs from the holotype in the shape of wider umbilicus (uw/dm = 0.34). It differs from the holotype probably owing to a longer pre-adult ontogenetic stage. While the holotype has just reached the stage in which the umbilical width is being reduced by increasing overlap the uw/dm ratio is reduced when compared with paratype GPIT-PV-63928. Both specimens are very similar in their strongly convex course of the growth lines and the presence of shell constrictions.

Paratype GPIT-PV-63960 with about 22 mm conch diameter also shows a strong umbilical overlap upon the preceding whorl (Fig. 91C). The specimen allows an insight into the course of internal shell thickening in the adult stage. This course is almost linear and slightly biconvex, in contrast to the growth lines, which run with a convex curve (Fig. 93J).

Many additional, well-preserved specimens are available. Two of them (MB.C.31189.1, MB.C.31190.1) are illustrated here (Fig. 92); they supplement the material from the type series and show largely the same morphological characters.

The suture line of paratype GPIT-PV-63961 shows a lanceolate external lobe and an almost identically shaped, approximately symmetrical adventive lobe. Both are separated by a nearly symmetrical, inverted U-shaped ventrolateral saddle (Fig. 93H).

A series of sectioned specimens (Fig. 93A–G) shows the variation of the species in terms of the different pace in the ontogenetic development of their conch morphology. In specimen BGR X4643 (Fig. 93A) a stronger overlap of the umbilicus with a conch diameter of 19 mm is not yet recognisable; however, half a volution later, at 22 mm in diameter, the overlap is very prominent and a shallow dorsolateral depression can be recognised.

Paratype GPIT-PV-63961 (Fig. 93B) and specimen MB.C.31179.1 (Fig. 93C) already show an incipient flattening of the whorl profile in the dorsolateral area at a conch diameter of 18 mm and a beginning of a stronger overlap upon the umbilicus. In contrast to this, in the specimens MB.C.31181.1 (Fig. 93D) and MB.C.31181.2 (Fig. 93F), such a tendency is not yet recognisable at all at a conch diameter of 15 mm.

Remarks

Weyerella molaris differs from W. reticulum in the absence of spiral lines. Weyerella lenis has a much more slender conch (ww/dm ~0.32 at 15 mm conch diameter in contrast to W. molaris with 0.50).

Species with similar conch morphology of the genus described from Guizhou have either a broader conch ( W. discoides with ww/dm ~0.60) or a more slender conch ( W. popanoides and W. mimica with ww/dm ~0.40) than W. molaris (ww/dm ~0.50). The material described by Ruan (1981) as W. molaris differs by the narrower umbilicus (uw/dm ~0.30) from the type material (uw/dm ~0.40) at 15 mm conch diameter. Therefore, it cannot be placed in this species.

Weyerella protecta from the Anti-Atlas is similar, but shows a narrowing of the umbilicus starting at a larger diameter. At 20 mm conch diameter, the uw/dm ratio is about 0.30 in W. molaris, but still about 0.38 in W. protecta .

Gattenpleura concava has similar juvenile whorls, but closes the umbilicus in the adult stage and possesses a conspicuous dorsolateral groove, which in W. molaris is only very incipiently developed.