16 
KOSTRIFEEA. 
habits of the animals: — Platypoda. The foot 
depressed, expanded for crawling. 2. Protopoda, 
Foot roundish, truncate, or clavate when the ani- 
mals are sedentary, living in shells attached to 
marine bodies. 3. Leptopoda, Foot compressed for 
leaping. 4. Heteropoda. The foot compressed, fin- 
like, with a small sucker for attaching itself to float- 
ing bodies. 
The British fluviatile and terrestrial species all 
belong to the first section, and form a division of 
it, characterised by having the eyes sessile, or nearly 
so, on the outer side of the bases of the subulate 
tentacles, and the mantle enclosed in the shell, which 
have been called Edriophthalma, Cochlea. 
These animals are divided into groups or families, 
according to the formation of the respiratory organs 
or gills j and position of the eyes, thus : — - 
1. Cyclostomidce. Eyes lateral, external; gills 
vascular. 
2. Littorinidce, Eyes lateral, external ; gills lami- 
nal ; operculum spiral. 
3. Bithiniadce. Eyes lateral, external ; gills lami- 
nar ; operculum annular. 
4. Viviparidce. Eyes lateral, external ; gills j^- 
lamentous ; operculum annular. 
5. Valvatidce. Eyes lateral, external ; gills sub- 
pinnate, exposed ; operculum spiral. 
6. Aciculidce. Eyes at the internal base of the 
tentacles ; operculum spiral. 
