All 20th century authors who have discussed this species in Utah have used the currently accepted scientific name Pupilla muscorum. Chamberlin and Jones (1929) applied to it the common name the two-toothed snail.
Although it is not clear whether any subspecies of this species are currently recognized, if subspecies do exist within this species, it would possibly be the type (or nominate) race, Pupilla muscorum muscorum, that occurs in Utah. The species, however, could well be considered monotypic.
Chamberlin and Jones (1929) mentioned: "A form known as Xerobia [sic] Pilsbry, commonly ranked as a subspecies, is reported to be the common form in Colorado." Seemingly, Chamberlin and Jones (1929), who noted "[w]e failed to take this species [in Utah]" and clearly had not seen material from this state, were implying that this species, in Utah, may be represented by the nominal race xerobia. Pilsbry (1948), who had earlier named the form xerobia, reversed his earlier opinion, stating that xerobia should "... be regarded as an arid station hunger form rather than a true race." In modern terms, xerobia would be called an ecomorph.
Status in Utah
Only 5 occurrences have been reported in Utah, all of them historical, these being in Utah County (Ingersoll 1877, Chamberlin and Jones 1929), Sevier County (Chamberlin and Berry 1930), Salt Lake County (Woolstenhulme 1942a), Grand County (Henderson 1936), and San Juan County (Henderson 1936).
Abundance of this species in Utah is not known. Chamberlin and Jones (1929) and Chamberlin and Berry (1930), did not provide information regarding specimens. Woolstenhulme (1942a) reported a "new record" based on 1 Utah specimen but did not indicate whether it was alive when collected or, perhaps, a very old, dead shell.
Threats to this species in Utah are not known but are thought not to be great. The population trend of this species in Utah is unknown.
Inventory is needed to determine whether this species, not reported in Utah since 1942 (and even then based on one specimen of unknown condition--perhaps an old dead shell), is extant in the state as well as to determine the extent of its distribution and abundance. It should be sought throughout the Wasatch Mountains and the central High Plateaus and in other mountainous areas of Utah.
As with other species in the family Pupillidae, this species is minute and living examples are difficult to find; thus, it is easily missed unless special efforts are made to discover it.
Habitats Utilized in Utah
Habitat information for this species in Utah is lacking. However, two of the reported localities are canyons descending west from the Wasatch Mountains (Chamberlin and Jones 1929, Woolstenhulme 1942a) and another is a moderately high (approximately 8,000-9,000 ft elevation) location in the central High Plateaus (Chamberlin and Berry 1930). Part of the locality data reported by Woolstenhulme (1942a) was "Stepping Stone Spring", which, though this species is terrestrial and would not have been in the spring itself unless it was dead (drift) material, suggests a moist, probably riparian site.