Large order of gastropods usually breathing by means of a lung-like sac comprising most land snails and slugs and many freshwater snails

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Pulmonata \Pul`mo*na"ta\, n. pl. [NL., from L. pulmo, -onis, a lung.] (Zo["o]l.) An extensive division, or sub-class, of hermaphrodite gastropods, in which the mantle cavity is modified into an air-breathing organ, as in Helix, or land snails, Limax, or ...

Wikipedia Word definitions in Wikipedia
Pulmonata , or "pulmonates", is an informal group (previously an order , and before that a subclass ) of snails and slugs characterized by the ability to breathe air, by virtue of having a pallial lung instead of a gill , or gills. The group includes many ...