Drop Snails (Family Helicinidae)
Globular Drop snail (Oligyra orbiculata Say, 1818)
Drop snails have a notable shape – like little "globs". Two species are named in the databases: the Cherrystone Drop snail, Hendersonia occulta (Say, 1831), and the Globular Drop snail Oligyra (Helicina) orbiculata Say, 1818.
There were two collections of the Cherrystone Drop snail from the opposite sides of the state along the southern border (several from Posey County up to the 1950s and one in Delaware County). There was a single recent collection (2015) of the Globular drop in Bartholomew County.
Dourson (2010) describes the structure and habitat of the drop snails in Kentucky which might work for Indiana. The Globular and Cherrystone Drops are about the same size, but the Globular drop has a rounded periphery (see image) and a light brownish band (may not always be there according to Oesch et al. 2013) .
While both species are calciphiles, the Cherrystone Drop favors "river bluffs, mixed hardwood talus slopes, ravines and mountainsides" while the Globular Drop is found in "more open habitat such as glades and limestone areas". It is also noted as a glade species in Missouri (Oesch et al. 2013).
Oesch et al. (2013) gives a key to distinguish the species, modified here:
Surface relatively smooth; color whitish to reddish cinnamon, usually with white band at the periphery - Oligyra orbiculata
Surface with coarse axial ridges; color uniform reddish brown to yellowish, without peripheral band - Hendersonia occulta
Cherrystone Drop snail
Hendersonia occulta (Say, 1831)
Globular Drop snail
Oligyra orbiculata Say, 1818