Discus whitneyi (Newcomb, 1864)

• Helix striatella Anthony 1840: 278, pl. 3, fig. 2, non Helix striatella Rang, 1831.
• Helix whitneyi Newcomb 1864: 118.
• Helix cronkhitei Newcomb 1865: 180.
• Patula ruderata cronkhitei f. viridula Cockerell 1890: 102, non-binomial.
• Pyramidula striatella catskillensis Pilsbry 1898 (1897–1898): 141, nomen nudum.
• Pyramidula striatella var. catskillensis Pilsbry 1898: 86.
• Pyramidula cronkhitei anthonyi Pilsbry in Pilsbry & Ferriss 1906: 153.

Identification. Shell subdiscoidal. Spire low. Whorls 4½–5, with periphery of last whorl subangular to convex. Protoconch smoothish perhaps very minutely granular. Teleoconch with sharp, rather regular, colabral ribs that continue undiminished in size onto base. Aperture subovate. Lip not thickened or only very slightly, simple; columellar lip a bit expanded. Umbilicus c. ¼–⅓ of shell width. Shell brown, slightly reddish brown or darker, with a silken sheen.

Animal pale grey. Head and tentacles darker grey or blackish; sides of foot with pale, with tiny brown speckles.

Comparison. This species is distinguished from D. shimekii by its smaller, more reddish than yellowish shell, with a well-ribbed base, and an umbilicus with less steep sides.

Habitat. Forests of all types, as well as some open habitats and drier parts of wetland habitats (marshes). Snails usually live under rocks, coarse woody debris, and logs and in leaf litter and vegetation.

Geographic distribution. In BC, common in northern and interior regions but rare along most of the coast. Widespread across boreal and temperate North America and known from every province and territory of Canada.

Etymology. Discus, from the Greek discos, a disc; the gender is masculine. This species was named after Josiah Dwight Whitney (1819–1896), an American geologist, professor of geology at Harvard University (from 1865), and chief of the California Geological Survey (1860–1874) (Wikipedia).

Remarks. Discus whitneyi was for many years known as D. cronkhitei (Newcomb, 1865). However, Roth (1988) demonstrated that D. whitneyi is an earlier name for the species. By using Article 23.9 of the Code (ICZN 1999), Helix whitneyi could have been declared a nomen oblitum and Helix cronkhitei a nomen protectum, but this was not done, and D. whitneyi was rapidly adopted as the accepted name and is now general use.

Some authors have suggested that the Palaearctic D. ruderatus is the same species (e.g. Dall 1905; Umiński 1962) and others have accepted this as fact (Kerney & Cameron 1979; Welter-Schultes 2012). However, these species were found to be separate in the molecular phylogenetic analysis by Salvador et al. (2020).

References

• Anthony JG (1840) Descriptions of three new species of shells. Boston Journal of Natural History 3: 278–279, pl. 3 figs 1–3.
• Cockerell TDA (1890) A list of the Mollusca of Colorado. The Nautilus 3: 99–103.
• Dall WH (1905) Land and fresh water mollusks. Doubleday, Page and Co., New York, New York, USA, 1–171, 2 pls.
• ICZN (1999) International Code of Zoological Nomenclature, Fourth Edition. The International Trust for Zoological Nomenclature, London, UK, pp. https://code.iczn.org/
• Kerney MP, Cameron RAD (1979) A field guide to the land snails of Britain and north-west Europe. Collins, London, United Kingdom, 288 pp, 24 pls.
• Newcomb W (1864) Descriptions of nine new species of Helix inhabiting California. Proceedings of the California Academy of Sciences 3: 115–119.
• Newcomb W (1865) Description of new species of land shells. Proceedings of the California Academy of Sciences 3: 179–182.
• Pilsbry HA (1898) [Catalogue of American land shells with localities]. The Nautilus 11: 138–144.
• Pilsbry HA (1898) Descriptions of new species and varieties of American Zonitidæ and Endodontidæ. The Nautilus 12: 85–87.
• Pilsbry HA, Ferriss JH (1906) Mollusca of the southwestern states. II. Proceedings of The Academy of Natural Sciences of Philadelphia 58: 123–175.
• Roth B (1988 “1987”) Identities of two Californian land mollusks described by Wesley Newcomb. Malacological Review 20: 129–130.
• Salvador RB, Brook FJ, Shepherd LD, Kennedy M (2020) Molecular phylogenetic analysis of Punctoidea (Gastropoda, Stylommatophora). Zoosystematics and Evolution 96: 397–410. https://doi.org/10.3897/zse.96.53660
• Umiński T (1962) Revision of the Palearctic forms of the genus Discus Fitzinger, 1833 (Gastropoda, Endodontidae). Annales Zoologici 20: 299–333.
• Welter-Schultes F (2012) European Non-marine Molluscs, a Guide for Species Identification. Bestimmungsbuch für europäische Land- und Süsswassermollusken. Planet Poster Editions, Göttingen, [3] + 679 + [78] pp.