GASTROPODA 507 



a single or of several pieces, but never of two symmetrical pieces; the 

 radula is broad, often nearly as broad as long, with many transverse 

 rows of veiy numerous teeth. These rows are either straight, curved, or 

 angulated. The pulmonate tooth has a broad base and a recurved and 

 either spine-like or dentate crown. 



The pulmonates are hermaphroditic animals, a single protandric gonad, 

 the hermaphroditic gland, being present. The aquatic forms have two 

 genital pores, while most land pulmonates have but one. The genital 

 tract is considerably more complex in some forms than in others. A few 

 snails bear living young, but most of them lay eggs, those of the land 

 forms having calcareous shells and being deposited in the ground and 

 other moist places, while those of the aquatic forms are surrounded by a 

 transparent jelly. 



The majority of the Pulmonata live on the land, either on the ground 

 among decaying leaves, in rotting wood, or in other dark moist placee, or 

 sometimes among the foliage of trees and shrubs. The aquatic forms are 

 fomid on vegetation or on muddy or sandy banks in streams and fresh- 

 water ponds and lakes; a few are marine. A few pulmonates are car- 

 nivorous, feeding on other snails and other small animals, but the great 

 majority live on vegetable substances. About 19,000 species of pulmonates 

 are known, which are grouped in two suborders. 



Key to the suborders of Pulmonata: 



Oi Aquatic pulmonates ; but 1 pair of tentacles 1. Basommatophora 



02 Land pulmonates ; 2 pairs of tentacles 2. Stylommatophoea 



Suborder 1. BASOMIVIATOPHORA. 



Fresh-water, or in a few eases marine or terrestrial, snails with 

 but 1 pair of tentacles (Fig. 776), which are solid and usually flattened, 

 and at the base of which are a pair of eyes; shell delicate, usually with 

 a conical spire and a large aperture ; 2 genital pores, usually on the right 

 side of the body, the male opening near the tentacle, the female opening a 

 little farther back, near the respiratory opening; ureter passes directly 

 forward from the kidney (Orthurethra) : cosmopolitan, there being about 

 4,000 species, grouped in 11 families. 



Key to the families of Basommatophora here described : 



(?! Shell spiral. 



&i Inner lip of aperture toothed 1. Auriculidae 



1>2 Lip smooth. 

 Ci Spire raised. 



d^ Shell right-handed 2. Lymn^idae 



d2 Shell left-handed 3. Physidae 



c^ Spire discoid 4. Planorbidae 



a. Shell conic, not spiral 5. Ancylidae 



