MONOTOCARDIA TAENIOGLOSSA 



413 



Fig. 273. — Solarium perspectivum 

 Lam., Eastern Seas. 



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

 operculum corneous, central tooth 

 ahsent, laterals and marginals num- 

 erous, long, and narrow; Flatyschismo 

 (Silurian), (ii.) Toriniinae. Genera : 

 Torinia, whorls usually rounded, 

 operculum (i'ig. 183) conically ele- 

 vated, spiral externally, central tooth 

 present, marginals few, edge pecti- 

 nated ; Omalaxis. (iii.) Euomiiha- 

 linae, shell planorbiform, whorls 

 rounded. Genera: Uuom2)hahis, Oj)hi- 

 leta, ScMzostoma, £cci/liom2)halus 

 (all Palaeozoic). 



Yam. 9. Homi(lofiyridae.. — Tentacles absent, eyes sessile, 

 central tooth unicuspid on a quadrangular base, laterals and 

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

 l)iform. Eecent. Single genus : Homalogyra, whose true position 

 is uncertain. 



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

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

 reproduction oviparous or ovoviviparous, radula very long ; shell 

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

 ous, nucleus excentrical. Jurassic . Principal genera : 



Littorina (radula. Fig. 16, p. 20), Cremnoconchus (p. 16), Fos- 

 sarina ; Tectarius, shell tubercled or spinose ; Bisella, 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, Fossanis. 



Fam. 12. Cydoijlioridac. — Ctenidium replaced by a pulmon- 

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

 shell variously spiral, peristome round, often reflected, operculum 



circular. Terrestrial only. Cretaceous . (i.) Pomatiasinae, 



shell high, conical, longitudinally striated, operculum consisting 

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

 Diidoviviatininae, shell more or less pupiform, peristome thick- 

 ened or reflected, often double. Genera ; Bijylommatina (subg., 

 Nicida, Palaina, Paxillus, Arinia'), shell dextral or sinistral, 

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



