Merica obsoleta (Hörnes, 1856), Grund

Harzhauser, Mathias & Landau, Bernard, 2012, A revision of the Neogene Cancellariid Gastropods of the Paratethys Sea 3472, Zootaxa 3472, pp. 1-71 : 29

Merica obsoleta (Hörnes, 1856)

Figs 6I 1–I 3, 6J 1–J 3

Cancellaria obsoleta Hörnes 1856: 678 , pl. 52, figs. 3a–b.

Cancellaria (a. Merica ) obsoleta M. Hoern. — Hoernes & Auinger 1890: 281.

Cancellaria (Ventrilia) obsoleta Hörnes — Sieber 1936: 92.

Trigonostoma (Ventrilia) obsoleta (Hörnes, 1856) — Harzhauser 2002: 112.

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

Studied material. 4 spec. Grund ( Austria) NHMW 1869 /0001/0282; 1 spec. Niederkreuzstetten ( Austria) NHMW 1861 /0002/0110.

Illustrated material. Figs 6I 1–I 3: specimen illustrated in Hörnes (1856, pl. 52, figs 3a–b), Grund ( Austria), height: 27.8 mm, width: 18.6 mm, NHMW 1869 / 0001/0282, designated herein as lectotype to allow a clear definition of this species; Figs 6J 1–J 3: Grund ( Austria), height: 24.9 mm, width: 17.6 mm, NHMW 1869 /0001/0282.

Description. This rare species is quite variable concerning spire height. Hörnes (1856) selected the specimen with the highest spire, whilst all other available shells have a depressed spire and a large, bulbous last whorl. The low protoconch is poorly preserved. Early teleoconch whorls develop a delicate cancellate sculpture formed by weak and densely spaced axial ribs overrun by weaker spiral threads. Soon, the axial ribs disappear and are replaced by wide spaced, poorly defined, low axial folds. The spiral ribs pass into about ten broad and also poorly defined and very low spiral cords accompanied by numerous delicate and very dense secondary and tertiary threads. The also extremely dense growth lines cross these threads resulting in a pitted microsculpture reminiscent of some epitoniids. The area between axial swellings and primary spiral cords may be slightly depressed; the suture is deep and narrowly canaliculate. Aperture broad ovoid with thin and smooth outer lip and callused inner lip; no umbilicus is developed and the siphonal canal is obsolete. The concave columella displays a rather weak central fold and an even weaker second swelling below.

Discussion. Aneurystoma canaliculata ( Janssen, 1972) , from the Middle Miocene of the North Sea Basin, differs in its smaller size, its stronger columellar folds and its prominent spiral ribs. Shells from the Burdigalian of Italy referred to as varieties of Cancellaria obsoleta Hörnes by Sacco (1894) and Ferrero– Mortara et al. (1984) are obviously not conspecific with the Paratethyan species, based on the huge umbilicus and squat outline.

Distribution. A very rare species which appears during the Karpatian and early Badenian in the Paratethys.

Paratethys —Karpatian: Waschberg Unit ( Austria: Niederkreuzstetten); Badenian: North Alpine Foreland Basin ( Austria: Grund).