Tribia mediangulata ( Sacco, 1894 )

Harzhauser, Mathias & Landau, Bernard, 2012, A revision of the Neogene Cancellariid Gastropods of the Paratethys Sea 3472, Zootaxa 3472, pp. 1-71 : 54-55

Tribia mediangulata ( Sacco, 1894)

Figs 3V, 10F 1–F 3

Cancellaria uniangulata Desh. — Hörnes 1848: 19 [non Cancellaria uniangulata Deshayes, 1830 ].

Cancellaria uniangulata Desh. —Hörnes 1854: 306, pl. 34, figs 2a–b [non Cancellaria uniangulata Deshayes, 1830 ].

Cancellaria (o. Trigonostoma ) uniangulata Dech. [sic]— Hoernes & Auinger 1890: 278 [non Cancellaria uniangulata Deshayes, 1830 ].

Cancellaria (Tribia) uniangulata var. mediangulata Sacco, 1894: 36 .

Cancellaria ( Trigonostoma ?) uniangulata Desh. — Sieber 1936: 88 [non Cancellaria uniangulata Deshayes, 1830 ].

Narona (Sveltia) uniangulata ( Deshayes, 1830) — Švagrovský 1982: 402, pl. 4, fig. 7 [non Cancellaria uniangulata Deshayes, 1830 ].

Narona (Tribia) uniangulata ( Deshayes, 1830) — Bałuk 2006: 214, pl. 16, fig. 2 [non Cancellaria uniangulata Deshayes, 1830 ].

non Cancellaria uniangulata Desh. — Friedberg 1914: 240, pl. 15, figs 1a–b [=?].

non Cancellaria uniangulata Deshayes — Csepreghy-Meznerics 1950: 58, pl. 3, fig. 17 [= Sveltia dertovaricosa Sacco, 1894 ]. non Narona (Tribia) uniangulata ( Deshayes, 1830) — Bałuk 1997: 49, pl. 16, fig. 2 [=?].

Type material. NHM Vienna ( Austria); see below for details .

Studied and illustrated material. Figs 3V, 10F 1–F 3: syntype illustrated in Hörnes (1854, pl. 34, figs 2a–b), Gainfarn ( Austria), height: 19.8 mm, width: 10.8 mm, NHMW 1852 /0012/0040.

Description: This very rare species is characterised by a strongly gradate spire composed of sharply angular whorls, with a broad, almost flat, downwards sloping sutural ramp and flat-sided whorls below the periphery, tapering inwards to the abapical suture. The axial ribs are prominent (about 15 appear on the last whorl) without forming spines. The spiral sculpture is strongly reduced and consists of weak spiral cords below the shoulder, only clearly developed where they overrun the axial ribs. The last whorl contracts rapidly below the shoulder angulation and is nearly flat-sided. Its protoconch consists of 1.75 whorls which are rapidly increasing in diameter and strongly convex.

Discussion. The shells have usually been identified as Tribia uniangulata ( Deshayes, 1830) , a Late Miocene and mainly Pliocene Mediterranean species ( Brunetti et al. 2006). Only Sacco (1894) proposed to treat the Viennese specimens as Tribia uniangulata var. mediangulata . This distinction does indeed seem justified. Differences are the steep sutural ramp and the much weaker, but more numerous, axial ribs of Tribia mediangulata . Moreover, its lower half of the last whorl and base are conical with feebly convex surface but broad and convex in T. uniangulata (cf. Chirli 2002). A comparison with shells from the Pliocene of Asti in Italy in the collections of the NHM revealed that the protoconch of T. mediangulata is slightly higher and its diameter increases much slower. Brunetti et al. (2006) provide a survey of the Pliocene–Pleistocene species of Tribia from the Mediterranean Sea. Among these, Sveltia uniangulata var. dertolyratoides Sacco, 1894 , from the Tortonian of Stazzano in Italy, is comparable with T. mediangulata concerning the conical shape of the last whorl and the sutural ramp. Differences are the prominent and wide spaced axial ribs, the weak spiral sculpture and the lower spire of the Italian shell. The Pliocene Tribia angasi ( Crosse, 1863) is another species resembling T. mediangulata . It is clearly distinguished from the Miocene species by its paucispiral protoconch, the wide spaced axial ribs and lacks the prominent lirae within the outer lip.

The specimens from the Polish–Carpathian Foredeep, identified as Tribia uniangulata by Friedberg (1914) and Bałuk (1997) are not conspecific with the shells from the Vienna Basin. These differ in their stout outline, strong spiral sculpture and especially in the low and broad protoconch and broad early teleoconch. The Polish shell in Bałuk (2006), however, fits well to Tribia mediangulata ( Sacco, 1894) .

Distribution. A rare Paratethyan species which appears during the early Badenian and persists into the late Badenian (found at Borský Mikuláš in Czech Republic).

Paratethys —Badenian: Polish–Carpathian Foredeep ( Poland: Korytnica); Vienna Basin ( Czech Republic: Borský Mikuláš; Austria: Gainfarn, Steinebrunn).