Discus (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 1890b: 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 to low. Spire low-conical. Whorls 4½–5, with periphery of last whorl subangular to convex. Protoconch smoothish [perhaps minutely granular]. Teleoconch with sharp, rather regular, colabral ribs that continue undiminished in size onto the base. Aperture rounded to subovate. Lip not thickened, simple. Umbilicus ca ¼–⅓ of shell width. Shell dark, brown, with a silken sheen.
Animal pale grey; head and tentacles are darker grey or blackish; sides of foot with pale, brown speckles.
Habitat. Forests of all types, and in open habitats, including tundra and drier parts of marshes; usually under rocks, dead wood, and debris, and in leaf litter and vegetation.
Canadian range. Nearly ubiquitous, known from every province and territory.
Etymology. 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).
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 is general use.
Pilsbry (1948) recognized a subspecies, D. cronkhitei catskillensis (Pilsbry, 1898), based on presence of a distinctly angular periphery. For many years, the taxonomic validity of this taxon was uncertain. Hubricht (1963, 1985), and most authors since, have regarded it to be a full species, but its acceptance as a full species was never universal. There has been a little some inconsistency in distinguishing between D. whitneyi and D. catskillensis in collections as well as the literature, and indeed, slightly more angular juvenile D. whitneyi are sometimes identified as D. catskillensis. Based on material from across Canada, preliminary results of DNA barcoding of carinate and non-carinate specimens of D. catskillensis/whitneyi suggest that these are all one species (Nicolai & Forsyth unpublished). So, at least as identified in Canada, only one species is present. No individuals were included from the type localities of either species.
Turgeon et al. (1998) gave the date of publication of D. catskillensis as 1896. However, Pilsbry first described Pyramidula cronkhitei catskillensis in a paper published in The Nautilus on 2 December 1898 (Pilsbry 1898, Clench & Turner 1962).
Some authors have suggested that the Palaearctic D. ruderatus (A. Férussac, 1821) is the same species (e.g. Dall 1905, Umiński 1962) and others have accepted this as fact (Kerney & Cameron 1979, Welter-Schultes 2012); no one has, however, presented clear evidence that they are the same species. Thus, D. whitneyi is retained for now.