Wollastonia subcarinulata (Wollaston, 1878), comb. n.

Mattia, Willy De, Neiber, Marco T. & Groh, Klaus, 2018, Revision of the genus-group Hystricella R. T. Lowe, 1855 from Porto Santo (Madeira Archipelago), with descriptions of new recent and fossil taxa (Gastropoda, Helicoidea, Geomitridae), ZooKeys 732, pp. 1-125 : 59-61

† Wollastonia subcarinulata (Wollaston, 1878), comb. n. stat. n. Figs 196-198, 199

List of synonyms.

1878 Helix (Hystricella) oxytropis var. ss subcarinulata Wollaston: 168.

Discula (Hystricella) oxytropis subcarinulata - Waldén: 267.

2002 Geomitra oxytropis subcarinulata - Bank et al.: 124.

2006 Discula oxytropis - Cameron et al.: 49 (1): 40 [partim].

2009 Hystricella oxytropis subcarinulata - Groh et al.: 21, fig. 27.

Type material.

NMWC 80.202, Acc 55.158, lectotype (herewith designated), from loc. typ., ex coll. Melvill-Tomlin, ex coll. T. V. Wollaston, Porto Santo, Madeira (Fig. 196).

Further material examined.

All from Porto Santo, CKG/2, Barbinha, Quaternary aeolinites, layer 3, 33°04'04"N / 16°17'49"W, 8 m, leg. K. & C. Groh, Jul. 4 1983 and Jul. 5 1983; CKG/3, Barbinha, Quaternary aeolinites, layer 2, 33°04'04"N / 16°17'49"W, 8 m, leg. K. & C. Groh, Jul. 4 1983 and Jul. 5 1983; CKG/8, Barbinha, Quaternary aeolinites, layer 4, 33°04'04"N / 16°17'49"W, 8 m, leg. K. & C. Groh, Jul. 4 1983 and Jul. 5 1983; CKG/2, south coast, ditch at the in 1985 new built harbour E Vila Baleira, lens of Quaternary calcareous aeolinite within a marine sandy beach terrace (nowadays beyond the quay of the harbour), 33°03'50"N / 16°18'56"W, 0-1.5 m, leg. J. Gerber, K. Groh & J. Hemmen, Aug. 1985; CWDM/8, Porto Santo, excavated mud walls behind the cart speedway E of the new harbour of Porto Santo, 33°03'48"N / 16°18'22"W, 30 m, leg. W. De Mattia & J. Macor, May 24 2015; CWDM/9, E of Vila Baleira, S slope of the hill above Vale do Touro, 50 m W of the oil tanks, excavated Quaternary mixed gravel, 33°03'47"N / 16°19'26"W, 24 m, leg. W. De Mattia & J. Macor, May 24 2015; CWDM/20, Pico do Baixo, E entrance of the tunnel, Quaternary mud deposit, 33°03'44"N / 16°17'45"W, 20 m, leg. W. De Mattia & J. Macor, May 24. 2015.

Locus typicus.

Porto Santo, Madeira.

Original description.

From Wollaston 1878: var. β. subcarinulata - Major, spira magis elevata, ad apicem paulo magis acuta, anfractibus in medio obsolete subcarinulato. - Long. axis 2½ lin.; diam. 3½.

Redescription of shell.

Shell large for the genus, with 5.9 regularly increasing whorls, the protoconch with 2.5 whorls. The form of the shell is flat conical, the slightly convex teleoconch whorls separated by a rather shallow but distinct, simple suture. The body whorl shows a distinct, rounded keel, which is enforced by a concave impression below the periphery. The last whorl measures 70%, the penultimate whorl 10% of the total shell height. The lower part of the body whorl is beneath the significantly marked periphery in frontal view first significantly concave, later moderately convex. The keel of the body whorl is located in the upper part of its total height. The aperture, which is inclined to the vertical axis of the shell in an angle of 69° and is descending in its last 5% in an angle of 36° to the horizontal axis, is horizontally elliptic; towards the umbilical region a bit flattened. Its width measures 45% of the total shell width and its height 44% of the total shell height. It has a peristome that is completely detached from the body whorl. The lip is distinctly reflected and very wide at its basal and columellar sides. The eccentric umbilicus, which measures 13% of the total shell width, is shaped like a pinhole in the penultimate whorl and is completely closed in the earlier whorls. The protoconch is smooth, the teleoconch shows a number of oblique radial ribs, 10 in the penultimate quadrant of the body-whorl and is additionally covered by numerous small, round tubercles. The number of tubercles in the standard-quadrate of the base is 108. There is a yellowish hue of colouration in the teleoconch; the keel usually distinctly lighter in colour. See Figs 197-198.

Measurements.

D 8.3 ± 0.3 mm (range 8.0-8.8 mm); H 6.1 ± 0.3 mm (range 5.8-6.4 mm); FW 4.1 ± 0.2 mm (range 3.9-4.2 mm); PA 48.2 ± 5.4° (range 42.6-54.4°); DU 0.6 ± 0,06 mm (range 0.5-0.7 mm); NT> 100; NW 5.6 ± 0.1 (range 5.5-5.7) (n = 25). Ratio D/H 1.4; ratio FW/H 0.5.

Distribution.

Wollastonia subcarinulata is known from the Quaternary mud and slope deposits along the southern slopes of the eastern part of Porto Santo, from Vale do Touro to the area around the tunnel of Ponta da Galé beneath Pico do Baixo. See map in Fig. 199.

Comparison and comments.

Wollastonia subcarinulata can be confused with other, rather large-sized species of the genera Hystricella and Wollastonia like H. echinoderma , W. vermetiformis and W. falknerorum sp. n., from which it can be distinguished, however, by the lack of a second keel, the rounded shape of the keel and a much finer sculpture as well as a more depressed conical form. From similar sized W. inexpectata it is distinguishable by the wider umbilicus, a flatter form, the keeled instead of angled periphery and a coarser granulation. From the recent W. oxytropis it can be distinguished by the larger size, the wider umbilicus, the more convex teleoconch whorls that are separated by a more distinctly marked suture, the finer granulation, and the wider aperture.

Taxonomic remarks.

The species is included in the genus Wollastonia because of its size and surface sculpture that is similar to W. oxytropis , as a variety of which it was described by Wollaston (1878). Subsequent authors, except Cameron et al. (2006), recognised the taxon as a subspecies of W. oxytropis .

Status and conservation.

Extinct before the islands’ scientific exploration in the 19th century, possibly already before human settlement.