The “Keyhole Limpets” and “Slit Limpets” (_Fissurellidæ_) resemble in external shape ordinary Limpets, but are perforated at or near the apex, or more or less slit at the front margin. The hole or slit gives passage to a tubular fold of the mantle, through which the water apparently flows to the gills. The largest species are from California and South America, and others are found, but not abundantly, on most shores. The animal of the large _Lucupina crenulata_ from California is eight or ten inches in length, and almost conceals the shell, and the shell of the South-African _Pupillæa aperta_ is also all but hidden beneath the mantle of the animal. [Illustration: Fig. 5.[3] _Pleurotomaria adansoniana._ Case 9. ⅓ natural size. ] [Sidenote: Case 9.] The _Pleurotomariæ_ are extremely rare in recent times, only five species being known, whereas over a thousand fossil forms have been described. The specimens of _P. adansoniana_ and _P. beyrichi_ exhibited in case 9, are among the finest acquisitions to the shell collection of recent years. [Sidenote: Cases 9–11.] The “Ear-shells” or “Ormers” (_Haliotidæ_) are found adhering to rocks in most parts of the world, with the exception of South America. They are lined with _pearl_, and many exhibit splendid colours and sculpture externally. Like the Limpets they hold on to the rocks with such tenacity that it is absolutely impossible to remove some of the larger species by force without injuring the shell. Boiling water or mustard and water poured over them will, however, soon compel them to relinquish their hold. The shell of _Haliotis_ is pierced by a series of holes parallel with the left margin. Through such of them as are open the animal protrudes a slender filament or feeler, and the water also finds its way through them to the gills beneath. The Single British species (_H. tuberculata_) is not actually found on the English coast, but common on rocks and stones at low-water in the Channel Islands. It is frequently eaten by the poor of those islands and the north of France; other species in New Zealand, China, Japan, West Africa, and elsewhere, constitute a common article of diet among the natives. _Haliotis_-shells are largely used in the manufacture of pearl ornaments, and in all kinds of inlaid work. [Illustration: Fig. 6. Top-shell (_Turbo petholatus_). (From the Indo-Pacific Ocean.) _a._ Inner surface of operculum. _b._ Exterior of ditto. ] [Sidenote: Cases 12–18.]