Discus (Antediscus) shimekii (Pilsbry, 1890)
- Zonites shimekii Pilsbry 1890a: 3.
- Pyramidula cockerelli Pilsbry 1898: 85.
- Zonitoides randolphi Pilsbry 1898: 87.
Identification. Shell subdiscoidal, a little more elevated than D. whitneyi. Spire low, conical. Whorls regularly enlarging. Whorls rounded in adults. Periphery rounded, median. Protoconch smooth. Teleoconch with narrow colabral riblets, which seldom extend strongly onto noticeably smoother base. Aperture subovate, wider than high, edentulous. Lip not simple, normally thin (or rarely scarcely thickened). Umbilicus ca 2/7 of shell width. Shell opaque, matte, yellowish brown. Shell small, width to 6.5 mm wide (wider than high).
Habitat. In forests and tundra. Under dead wood, rocks, and vegetation, and in leaf litter.
Global range. Yukon, northern BC, south along the Rocky Mountains to New Mexico and Arizona. East to NWT (around Great Slave Lake), Cypress Hills and north-western arctic Ontario. Reported as Pleistocene fossils from the Loess of Iowa (Pilsbry 1948, Hubricht 1985).
Canadian range. Yukon, NWT (around Great Slave Lake, but not likely limited to just there), northern (Peace River region, northern Rockies, and Stikine region) and south-eastern British Columbia, Alberta (Rocky Mountain Foothills; along the Milk River at Writing-on-Stone Provincial Park (Forsyth & Lepitzki 2015), and in Cypress Hills (CMN unpubl. data). Oughton (1948) reported “slightly worn” shells from among stream drift collected in arctic Ontario at Fort Severn (Kenora District), speculating that they may be washed out Pleistocene fossils. Decades later, additional material was collected from stream drift of the Severn River and was reported by Forsyth & Oldham (2016). The best-preserved specimens still retain periostratum, which may not be exclude them from being Pleistocene fossils (periostracum may persist in fossils of this age).
Etymology. Named after Bohumil Shimek (1861–1937), who collected the original specimens. He was a life-long friend of Henry A. Pilsbry, with whom he began the study of shells during childhood. Shimek was professor of botany and curator of the herbarium at the University of Iowa.
Remarks. Pilsbry (1948) recognized the subspecies D. shimeki [sic] cockerelli (Pilsbry, 1898) for more flatly coiled shells having a shallower, broader umbilicus. However, Beetle (1957) noted variation in the breadth of the umbilicus and a gradual transition from low- to high-spired individuals, which Bequaert & Miller (1973) considered in treating cockerelli as a synonym of D. shimekii. Subspecies have not been used recently and are not used here.
The species name is frequently misspelled shimeki since at least Pilsbry (1948), but according to the Code (ICZN 1999), the original spelling Shimekii (Pilsbry 1898) should be emended to shimekii (ICZN 1999, Article 126.96.36.199), but the –ii termination must not be changed (Article 33.4).
- Beetle DE (1957) The Mollusca of Teton County, Wyoming. The Nautilus 71: 12–21.
- Bequaert JC, Miller WB (1973) The mollusks of the arid southwest with an Arizona checklist. University of Arizona Press, Tucson, xiv + 271 pp.
- Forsyth RG, Lepitzki DAW (2015) Terrestrial snails (Gastropoda: Pulmonata) from Writing-on-Stone Provincial Park, Alberta, Canada. Check List 11: 1636.
- Forsyth RG, Oldham MJ (2016) Terrestrial molluscs from the Ontario Far North. Check List 12: 1881.
- ICZN (1999) International Code of Zoological Nomenclature. Fourth edition. The International Trust for Zoological Nomenclature, London, UK.
- Oughton J (1948) A zoogeographical study of the land snails of Ontario. University of Toronto Studies, Biological Series 57: xii + 126 +  pp.
- Pilsbry HA (1890) Two new species of U.S. land snails. The Nautilus 4: 3–4.
- Pilsbry HA (1898) Descriptions of new species and varieties of American Zonitidæ and Endodontidæ. The Nautilus 12: 85–87.
- Pilsbry HA (1948) Land Mollusca of North America (north of Mexico). Vol. II, Part 2. The Academy of Natural Sciences of Philadelphia, Monographs 3: i–xlvii + 521–1113.