This key is based on major shell characters and will first take you to major groups of snails based on major differences in shell morphology. Then, it will follow through to smaller groups of species and , when possible, to an individual species.
The main characters used are primarily those described in the “Snail Structure” section, plus others as needed. Familiarize yourself with those.
The first "cut" is into 8 major groups - 7 with shells and the eighth is the slugs. Remember that images are NOT to scale.
Shell taller than wide; lip simple or slightly reflected, no teeth; bulimoid, columnar, conical, fusiform, or succiniform, ~2 to >20 mm (Go to Group A key)
includes: Cochlicopa, Columella, Pomatiopsis, Rabdotus, Succineidae
Shell taller than wide; reflected lip; lip reflected to thick, one or more tooth, columnar to pupilliform (Go to Group B key)
includes: Carychium, Gastrocopta, Pupillidae, Vertigo
Group C. Beehive to domed to roundish shape (Go to Group C key)
includes: Euconulus, Helicinidae, Strobilops, Ventridens
Wider than tall; reflected lip, umbilicate or rimate (Go to Group E key)
lip is reflected, spire more globose to depressed, teeth vary, umbilicus varies from rimate to open to widely open umbilicus
includes: Mesodon (in part), Allogona, Triodopsis, Daedalochila, Vallonia
Wider than tall; reflected lip, imperforate (Go to Group F key)
spire subglobose to subglobose/depressed; umbilicus imperforate
includes: Mesodon (in part), Neohelix, Patera (in part), Webbhelix, Xolotrema
Wider than tall; simple lip (Go to Group G key)
includes: Anguispira, Haplotrema, Mesomphix, Oxychilus, Helicodiscus, Glyphyalinia, Discus, Nesovitrea, Zonitoides, Guppya, Hawaiia, Lucilla, Punctum, Striatura, Gastrodonta, Paravitrea
No shell – slugs (Go to Group Slug key)
includes: Arion, Deroceras, Limacus, Limax, Megapallifera, Pallifera, Philomycus