XIV MONOTOCARDI A — TAENIOGLOSSA 4 1 3 



rium, shell depressed, highly finished, angular at periphery, 

 operculum corneous, central tooth 

 absent, laterals and marginals num- 

 erous, long, and narrow; Platy- 

 sehisma (Silurian), (ii.) Toriniinae. 

 Genera: Torinia, whorls usually 

 rounded, operculum (Fig. 183) 

 conically elevated, spiral externally, 

 central tooth present, marginals few, 

 edge pectinated; Omalaxis. (iii.) 

 Euomphalinae^ shell planorbiform, 

 whorls rounded. Genera: EuompTia- fig. 273.- Solarium perspectivum 



lus, Ophileta^ Schizostoma, Eccyliom- Lam., Eastern Seas. 



phalus (all Palaeozoic). 



Fam. 9. Homalogyridae. — Tentacles absent, eyes sessile, 

 central tooth unicuspid on a quadrangular base, laterals and 

 marginals replaced by an oblong plate ; shell very small, planor- 

 biform. Recent. Single genus : Homalogyra^ whose true posi- 

 tion is uncertain. 



Fam. 10. Littorinidae. — Proboscis short, broad, tentacles 

 long, eyes at their outer bases, penis behind the right tentacle; 

 reproduction oviparous or ovoviviparous, radula very long; shell 

 turbinate, solid, columella thickened, lip simple, operculum cor- 

 neous, nucleus excentrical. Jurassic . Principal genera : 



Littorina (radula. Fig. 16, p. -20), Cremnoconehus (p. 16), Fossa- 

 rina; Tectarius^ shell tubercled or spinose; Risella^ base slightly 

 concave ; Lacuna^ shell thin, grooved behind the columellar lip. 



Fam. 11. Fossaridae. — Shell turbinate, solid, small, white, 



spirally ribbed, outer lip simple. Miocene . Principal 



genus, Fossarus. 



Fam. 12. Cydophoridae. — Ctenidium replaced by a pulmo- 

 nary sac, tentacles long, thread-like (radula. Fig. 17, p. 21) ; shell 

 variously spiral, peristome round, often reflected, operculum 



circular. Terrestrial only. Cretaceous . (i.') Fomatiasinae, 



shell high, conical, longitudinally striated, operculum consisting 

 of two laminae united together. Single genus, Pomatias. (ii.) 

 Diplommatininae^ shell more or less pupiform, peristome thick- 

 ened or reflected, often double. Genera : Diplommatina (subg., 

 Nicida^ Palaina^ Faxillus, Arinia)^ shell dextral or sinistral, 

 small, columella often denticulated ; Opisthostoma (Fig. 208, p. 



