Mathilda clara Boettger, 1902

Harzhauser, Mathias & Landau, Bernard, 2023, The Architectonicidae and Mathildidae (Gastropoda, Heterobranchia) of the Miocene Paratethys Sea-victims of the Miocene Climatic Transition, Zootaxa 5370 (1), pp. 1-74 : 48-49

Mathilda clara Boettger, 1902

Figs 24A 1 –A 2

* Mathilda clara n. sp. — Boettger 1902: 155.

Mathilda clara Bttgr. —Boettger 1907: 168.

Mathilda clara Boettger — Cossmann 1912: 10.

Mathilda clara Boettger —Zilch 1934: 217, pl. 7, figs 11–12.

Mathilda clara Boettger, 1901 — Bałuk 1975: 114, pl. 13, fig. 9.

Type material. Lectotype (designated by Zilch 1934: 217): SMF 372692 (XII 2492a), SL: 2.9 mm, MD: 1.8 mm, Senckenberg Museum, Frankfurt/Main, Germany, Coşteiu de Sus ( Romania), illustrated in Zilch (1934: pl. 7, fig. 11), Figs 24A 1 –A 2 .

Additional material. SMF XII 2492b, Senckenberg Museum, Frankfurt/Main, Germany, Coşteiu de Sus ( Romania), illustrated in Zilch (1934: pl. 7, fig. 12) .

Revised description. Small, robust, stout conical shell; apical angle 35°. Protoconch multispiral, of about three smooth whorls, heterostrophic, deeply immersed in first teleoconch whorl, nucleus not exposed, tilted at angle of about 140°. Teleoconch of three angulated whorls separated by indistinct suture. Sculpture of three prominent spiral cords: S1 weakest, recessed; S2 most prominent, placed slightly above mid-whorl, forming slight keel at periphery; S3 slightly weaker than S2. Faint secondary spiral thread appears between S1 and S2 on concave sutural ramp on second teleoconch whorl. Fourth spiral cord at suture partially covered by subsequent whorl. Axial sculpture of 17 relatively broad, wide-spaced ribs forming cancellate pattern with spiral cords on the first two whorls, with large tubercles developed at intersections. Base rapidly contracting, flattened, with two weak peribasal spiral cords. Umbilicus reduced to narrow chink, but clearly delimited by low periumbilical cord. Aperture moderately large and wide, subpentagonal. Columella straight, tilted slightly to left. Columellar callus forming narrow rim. No parietal callus. Outer lip thin, crenulated.

Discussion. This species could be mistaken for a juvenile Mathilda praeclara Boettger, 1902 but is distinguished at the same growth stage by its distinctly wider spaced ribs, the much coarser tubercles developed at the sculptural intersections, and the surface on the last two whorls is less densely and sharply cancellate. The specimen from Korytnica ( Poland), described by Bałuk (1975), consists only of the protoconch and parts of the first teleoconch whorl but corresponds well to the type of M. clara .

Paleoenvironment. Unknown; probably middle to outer neritic.

Distribution. Only known from the Langhian equivalent of the Badenian in the Central Paratethys Sea.

Central Paratethys Sea. Badenian (Middle Miocene): Korytnica Basin: Korytnica ( Poland) ( Bałuk 2006); Făget Basin: Coşteiu de Sus ( Romania) ( Boettger 1902).

Figures

FIGURE 1. Descriptive terms used in descriptions of Architectonicidae (modified from Bieler 1993).

FIGURE 2. Whorl cross-sections of Architectonicidae genera. All modified after Bieler (1993) except for Simplexollata, Basisulcata and Ammotectonica. Solatisonax? refers to Solatisonax? kostejana (Boettger, 1907), Bold genera are represented in the Paratethys Sea. SSC: subsutural cord, MC: mid cord(s), UPC: upper peripheral cord, LPC: lower peripheral cord, IPC: infraperipheral cord; UC: umbilical crenae; PUC: proxumbilical cord.

FIGURE 24 A1–A2. Mathilda clara Boettger, 1902, lectotype, SMF 372692, Coşteiu de Sus (Romania). B1–B2. Mathilda praeclara Boettger, 1902, holotype, SMF 372690, Coşteiu de Sus (Romania).