4 I 6 MONOTOCARDIA TAENIOGLOSSA chap. 



Fam. 22. Adeorhidae. Eadula essentially rissoidan ; shell 

 depressed, circular or auriform, widely umbilicated, operculum 



corneous, paucispiral, nucleus excentrical. Pliocene . 



Principal genera : Adeorbis, Stenotis, Megalomphalus. 



Fam. 23. Viviparidae. — Snout blunt, tentacles long, right 

 tentacle in the male deformed, pierced with a hole corresponding 

 to the aperture of the penis, two cervical lobes, the right being 

 siphonal, foot with an anterior transverse groove ; teeth broad, 

 shallowly pectinate at the ends ; shell turbinate, whorls more or 

 less rounded, aperture continuous, operculum corneous, nucleus 

 sub-lateral, with a false sub-central nucleus on the external face. 



Animal ovo viviparous. Fresh water. Cretaceous . Genera : 



Vivipara ( = Faludina), subg., Cleopatra, Melantho, Tulotoma ; 

 Tylopoma (Tertiary), and Lioplax. 



Fam. 24. Valvatidae. — Branchia exserted, bipectinate, carried 

 on the back of the neck, a filiform appendage (Fig. 60, p. 159) on 

 the right of the neck, penis under the right tentacle, prominent, 

 eyes sessile, behind the tentacles ; radula like that of Vivipara ; 

 shell small, turbinate or flattened, operculum corneous, nucleus 

 central. Fresh water. Jurassic . Single genus, Valvata. 



Fam. 25. Ampullariidae. — -Snout with two tentacles, tentacles 

 proper very long, tapering, eyes prominently pedunculate, two 

 cervical lobes, the left siphonal, respiratory cavity divided by a 

 partition, a large branchia in the right chamber, the left func- 

 tioning as a pulmonary sac (Fig. 65, p. 158); radula large, 

 central tooth multicuspid, base broad, lateral and marginals falci- 

 form, simple or bicuspid ; shell large, turbinate or flattened, spire 

 small, whorls rounded ; operculum generally corneous, nucleus 

 sub-lateral, false nucleus as in Vivipara. Fresh water. Creta- 

 ceous . Single gexiViB Ampullaria (subg., Ceratodes, Facliy- 



lahra, Asolene, Lanistes, and Meladomus). 



Fam. 26. Cerithiidae. — Branchial siphon present, short, eyes 

 variable in position ; central tooth small, evenly cusped, lateral 

 hollowed at base, multicuspid, marginals narrow ; shell long, 

 turriculate, whorls many, generally tuberculate, varicose or spiny, 

 aperture sometimes strongly channelled ; operculum corneous, 

 sub-circular, nucleus nearly central. Marine or brackish water. 



Trias . Principal genera : Triforis, shell small, generally 



sinistral; Fastigiella, Cerithium (Fig. 12, p. 16), Bittiuni, Pota- 

 mides (subg., Tympanotomus, Pyrazus, Pirenella, Telescopium, 



