Stenotrema - Slitmouth Snails (Family Polygyridae)
Slitmouth snails are easily distinguished from other land snails. They are generally “pill shaped” but with a narrow slit-like aperture, a large and long parietal tooth, and a notch in their basal lip. The shell surface is often covered with hairs. They are superficially similar to Euchemotrema, the Pillsnails, which lack the notch.
Three species are more widespread: Stenotrema barbatum (Bristled Slitmouth Snail), Stenotrema hirsutum (Hairy Slitmouth Snail), and Stenotrema stenotrema (Inland Slitmouth Snail).
A fourth species, Stenotrema angellum (Kentucky Slitmouth Snail), has a very restricted distribution – southeast counties along the Ohio River - with all the specimens attributed to Hubricht (1958). Nature Serve (2021) states: "Originally described from Indiana, Kentucky, and Tennessee (Hubricht, 1958) and shown to be distributed there accordingly across several counties (Hubricht, 1985). Center of range in Kentucky with Indiana and Tennessee edge of range."
The species appear to share similar habitat – woodlands in and below rocky and woody debris with the "usual" assortment of micro-habitat variations.
Identification: This is a difficult group without fresh shells. It is difficult to merge the descriptions in Dourson (2010), CMNH (Hotopp et al. 2013), Oesch et al. (2013), Hubricht (1958), or Burch (1962) into an Indiana key - but I have tried. I have not seen all these species, so this key is a shot in the dark. Be sure to use the sources to evaluate where the key takes you.
1a. aperture more narrow - go to 2
1b. aperture wider - go to 3
2a. basal notch larger and interdenticular sinus deeper - Stenotrema stenotrema
2b. basal notch smaller and interdenticular sinus indistinct - Stenotrema angellum
3a. longer and more widely spaced hairs, interdenticular sinus indistinct - Stenotrema barbatum
3b. smaller and more closely spaced hairs, interdenticular sinus deeper - Stenotrema hirsutum