ORDERS AND FAMILIES. gi 



HALIOTID.E. Shell ear-shape ; spire flattened ; mouth large and pearly; 

 outer lip perforated, the perforations being successively filled up when 

 no longer required for the protrusion of the tentacles of the mantle. 

 Haliotis, 333. 



HOMALOGYRID/E. Shell a small, flat coil, with involute spire ; whorls 

 angulated; operculum with few whorls and a central nucleus. 

 Homalogyra, 385, 386. 



HYDROBIID^;. Shell conical, small, smooth ; mouth entire ; an umbilical 

 cleft ; eyes at the base of the tentacles. Hydrobia, 426 to 429 ; Bithynia, 

 430, 431- 



IANTHINID^;. Shell heliciform, violet in colour, thin, translucent, fragile ; 

 whorls few and ventricose ; mouth four-sided. lanthina, 357 to 359. 



JEFFREYSIID.E. Shell minute, translucent, smooth, and glossy ; mouth 

 oval or roundish ; operculum with marginal nucleus divided by an 

 inner rib. Jeffrey$ia, 435 to 437. 



LAMELLARIID/E. Shell more or less internal ; ear-shaped or cap-shaped, 

 thin, pellucid, and fragile ; spire very small, mouth large, no oper- 

 culum. Lamellaria, 377; Velutina, 378, 379. 



LEPETID^;. Shell limpet - shaped, crown central or nearly central. 

 Lepeta, 322 ; Propilidium, 323. 



LITTORINID^E. Shell strong and never pearly ; pillar thickened ; mouth 

 rounded and entire ; operculum horny, thin, ear-shaped, nucleus 

 excentrical. Littorina, 387 to 391 ; Lacuna, 392 to 396. 



MARGINELLID^E. Shell oval, polished ; mouth truncated, narrow, 

 channelled at base only, and nearly as long as shell ; outer lip 

 thickened, pillar with few oblique folds. Marginclla, 529. 



MURICID/E. Shell having a straight anterior canal, and being oblong and 

 solid and tuberculate, spiny or varicose ; spire produced ; mouth 

 oval ; pillar not twisted. Trophon, 503 to 505 ; Murex, 506, 507 ; Pur- 

 pura, 508, 509 ; Lachesis, 510. 



NASSID^.- Sheiroblong, small ; spire turreted; canal short and abrupt; 

 outer lip thickened, often toothed ; operculum horny. Nassa, 513 

 to 516. 



NATICID/E. Shell globular, thick, smooth, few whorls, and small spire ; 

 outer lip simple; large umbilicus; operculum horny and calcareous. 

 Natica, 370 to 376. 



NERITID/E. Shell globular, thick ; spire small ; mouth semi-lunate, side 

 near pillar being expanded ; operculum calcareous, with prominent 

 apophyses on interior face, one of which locks behind the lip of the 

 pillar. Neretina, 356. 



PATELLID^E. Shell conical with apex turned forwards; mouth forming 

 entire base of cone. Patella, 324 ; Helcion, 325. 



PLEUROTOMARIIDJE. Shell trochiform with sinus band extending nearly 

 to apex ; umbilicus deep ; operculum horny, circular and multi-spiral, 

 nucleus central. Scissurella, 334. 



