Classification
Here is how the classification works:
Phylum->Class->Sub-class->Order->Sub-order->Infra-order->Superfamily->Family->Subfamily->
Genus->Subgenus->species->sub-species.
Landsnails belong to the phylum Mollusca,which has about 80.000 species in it.
The first research into classification focused on the shape of the shell.Later when people got to know the 
internal organs more groups were named.The most extensive 
classification was made by J.Thiele in 1929-1935.Three sub-classes were named:
Prosobranchia
Ophistobranchia
Pulmonata.
Each order represented a higher stadium of evolution.
All malacologists used this classification.But later research revealed some weak points.
Because research continues the classification can't be permanent.I realize there are
people who might disagree with this classification.I tried to make a workable basis
for this site.
Please note:because this site deals with land-,freshwatersnails and slugs, only information about these groups is listed. 

Phylum Mollusca (mollusks) Class Gastropoda Subclass Pulmonata Order Acteophila Superfamily Elloboidea Family Carychiidae Family Ellobiidae Superfamily Melampidoidea Family Melampidae

Order Lymnophila Superfamily Acroloxoidea Family Acroloxidae Family Lymnaeidae Superfamily Physoidea Family Physidae Superfamily Planorboidea Family Planorbidae

Order Stylommatophora Suborder Heterurethra Superfamily Athoracophoroidea Family Athoracophoridae Superfamily Succineoidea Family Aillyidae Family Succineidae

Suborder Mesurethra Superfamily Clausiloidea Family Clausiliidae Family Cerionidae Family Megaspiridae Superfamily Strophocheiloidea Family Strophocheilidae Family Dorcasiidae Family Megalobulimidae

Suborder Orthurethra Superfamily Achatinelloidea Family Partulidae Family Achatinellidae Superfamily Cochlicopoidea Family Amastridae Family Cochlicopidae Superfamily Pupilloidea Family Buliminidae Family Cerastuidae Family Chondrinidae Family Enidae Family Orculidae Family Pleurodiscidae Family Pupillidae Family Pyramidulidae Family Strobilopsidae Family Valloniidae Family Vertiginidae

Suborder Sigmurethra Infraorder Aulacopoda Superfamily ?Testacelloidea Family Testacellidae Superfamily Arionoidea Family Arionidae Family Philomycidae Family Punctidae Family Helicodiscidae Family Endodontidae Family Charopidae Family Otoconchidae Family Discidae Family Thyrophorellidae Superfamily Limacoidea Family Agriolimacidae Family Ariophantidae Family Boettgerillidae Family Cystopeltidae Family Daudebardiidae Family Vitrinidae Family Euconulidae Family Helixarionidae Family Limacidae Family Milacidae Family Otoconchidae Family Parmacellidae Family Systrophiidae Family Thyrophorellidae Family Trigonochlamydidae Family Trochomorphidae Family Urocyclidae Family Zonitidae Infraorder Holopoda Superfamily Polygyroidea Family ?Ammonitellidae Family Polygyridae Family Corillidae Family Thysanophoridae Superfamily Oleacinoidea Family Testacellidae Family Oleacinidae Family Sagdidae Superfamily Helicoidea Family Bradybaenidae Family Camaenidae Family Helicellidae Family Helicidae Family Helminthoglyptidae Family Humboldtianidae Family Hygromiidae Family Oreohelicidae Family Solaropsidae Family Sphincterochilidae

Suborder Sigmurethra Infraorder Holopodopes Superfamily Achatinoidea Family Achatinidae Family Ferussaciidae Family Subulinidae Family Spiraxidae Superfamily Rhytidoidea Family Acavidae Family Caryodidae Family Chlamydephoridae Family Haplotrematidae Family Macrocyclidae Family Plectopylididae Family Rhytididae Superfamily Streptaxoidea Family Streptaxidae Family Systrophiidae Superfamily Bulimuloidea Family Amphibulimidae Family Bulimulidae Family Coelociidae Family Microceramidae Family Odontostomidae Family Orthalicidae Family Urocoptidae

Order Systellommatophora Superfamily Veronicelloidea Family Veronicellidae

Subclass Eogastropoda (Ponder & Lindberg, 1996) Subclass Orthogastropoda Ponder & Lindberg, 1996 Superorder Neritaemorphi Koken, 1896 Order Neritopsina Cox & Knight, 1960 Superfamily Neritoidea Family Helicinidae Family Neritidae Family Neritopsidae Superorder Caenogastropoda Cox, 1960 Order Architaenioglossa Haller, 1890 Superfamily Ampullarioidea J.E. Gray, 1824 Family Ampullariidae Family Viviparidae Family Bithyniidae Family Hydrococcidae Superfamily Cyclophoroidea J.E. Gray, 1847 Family Cyclophoridae Family Diplommatinidae Family Liareidae Family Poteriidae Family Pupinidae Family Maizaniidae Family Megalomastomidae Order Sorbeoconcha Ponder & Lindberg, 1997 Suborder Hypsogastropoda Ponder & Lindberg, 1997 Infraorder Littorinimorpha Golikov & Starobogatov, 1975 Superfamily Littorinoidea Family Annulariidae Family Pomatiasidae Superfamily Rissooidea Family Aciculidae Family Hydrobiidae Family Pomatiopsidae Superorder Heterobranchia J.E. Gray, 1840 Order Heterostropha P. Fischer, 1885 Superfamily Valvatoidea Family Valvatidae

For a description of the Subclass Pulmonata go here: The Pulmonates Main page