152 THE GASTROPODA 



sory organs are rarely found on the genital ducts, but are present in Palu- 

 dina, Cyclostoma, the Naticidae, Calyptraeidae, etc. Mandibles are usually 

 present. The intestine is long. The Platypoda form the largest group 

 of the Mollusca, comprising nearly sixty families of unequal value, some of 

 which are not thoroughly well known from an anatomical point of view. 

 FAMILY 1. PALUDINIDAE, d'Orbigny. Ctenidium monopectinate ; pedal 

 centres in the form of ganglionated cords ; the kidney is provided with a 

 ureter ; viviparous ; fluviatile. Genera Paludina, Lamarck. Neo- 

 thauma, Smith ; from Lake Tanganyika. Tylopoma, Brusina ; from the 

 Tertiary. FAMILY 2. CYCLOPHORIDAE, Gray. Pallial cavity devoid of a 

 ctenidium and transformed into a lung ; pedal centres in the form of 

 ganglionated cords ; otocysts with otoconia ; aperture of the shell and 

 the operculum circular ; terrestrial. Genera Pomatias, Hartmann ; shell 

 turriculated. Diplommatina, Benson. Hybocystis, Benson. Cyclophorus, 

 Montfort ; shell umbilicated, with a short spire and horny operculum. 

 Cyclosurus, Morelet ; shell uncoiled. Dermatoc&ra, Adams ; foot provided 

 with a horn-shaped protuberance at its posterior end. Spiraculum, Pear- 

 son ; aperture provided with a sutural tube at its superior angle. FAMILY 

 3. AMPULLARIIDAE, Gray. A monopectinate ctenidium present, and to 

 the left of it a pulmonary sac, separated from the ctenidium by an incom- 

 plete septum ; oesophageal nerve -collar in front of the buccal bulb ; 

 penis pallial ; amphibious. Genera Ampullaria, Lamarck ; visceral 

 sac and shell coiled dextrally. Lanistes, Montfort ; shell sinistral ; spire 

 short or obsolete. Meladomus, Swainson ; shell elongated, sinistml. 

 FAMILY 4. LITTORINIDAE, Gray. Ctenidium monopectinate ; oesophageal 

 pouches present ; pedal nerve- centres concentrated; a pedal penis near 

 the right tentacle. Genera Littorina, Fe"russac ; shell not umbilicated ; 

 foot devoid of appendages ; marine forms of semi-aerial habit (Fig. 85). 

 Lacuna, Turton ; foot with two posterior appendages ; marine forms of 

 exclusively aquatic habit (Fig. 7). Cremnoconchus, Blandford ; shell umbili- 

 cated; of exclusively aerial habit ; Indian. Risella, Gray. Tectarius, Valen- 

 ciennes. FAMILY 5. FOSSARIDAE, Fischer. Shell turbinated and umbili- 

 cated ; head with two cephalic lobes, as in some Rhipidoglossa. Genus 

 Fossarus, Philippi. FAMILY 6. PURPURINIDAE, Zittel. An exclusively 

 fossil family ; shell thick, with prominent spire, angular whorls, and oval 

 aperture. Genera Purpurina, d'Orbigny ; Jurassic. Brachytrema, 

 Morris and Lycett ; Jurassic. Scalites, Conrad ; Ordovician* FAMILY 7. 

 PLANAXIDAE, Adams. Shell not umbilicated, with pointed spire ; the 

 external border of the shell sharp ; a short pallial siphon. Genus 

 Planaxis, Lamarck. FAMILY 8. CYCLOSTOMATIDAE, Pfeiffer. Pallial 

 cavity transformed into a lung ; pedal centres concentrated ; otocysts 

 with otoliths ; no mandibles ; a deep longitudinal pedal groove present ; 

 terrestrial. Genera Cyclostoma, Draparnaud ; shell turbinated ; opercu- 

 lum calcareous ; British. Omphalotropis, Pfeiffer ; shell turriculated ; 

 operculum horny. FAMILY 9. ACICULIDAE, Gray. Shell narrow and 

 elongated ; operculum horny ; pallial cavity a pulmonary chamber ; 

 otocysts with otoconia. Genus Acicula, Hartmann. FAMILY 10. 

 VALVATIDAE, Gray. Ctenidium bipectinate, free throughout its length ; a 

 pallial filament on the right side ; hermaphrodite ; fluviatile. Genus 



