4l6 MONOTOCARDIA — TAENIOGLOSSA chap. 



Fam. 22. Adeorhidae. — Radula essentially rissoidan ; shell 

 depressed, circular or auriform, widely umbilicated, opercu- 

 lum corneous, paucispiral, nucleus excentrical. Pliocene . 



Principal genera : Adeorhis^ Stenotis, 3Iegalom2ohalus. 



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 ovoviviparous. Freshwater. Cretaceous . Genera: 



Vivipara (= Paliidma)^ subg., Cleopatra^ Melaiitho^ Tidotoma; 

 Tylopoma (Tertiary), and Ziioplax. 



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

 on the back of the neck, a filiform appendage (Fig. QQ^ 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. Ampullar iidae. — Snout with two tentacles, ten- 

 tacles 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 

 functioning 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. 



Cretaceous . Single genus, Ainpidlaria (subg., Ceratodes^ 



Paeliylahra^ 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), 

 Bittium^ Potamides (subg., Tympanotomiis^ Pyrazus^ Pirenella, 

 Telescopium^ Cerithidea, Lampania, all brackish water), Diastema 



