(laslfojiixlit . 



•i:\ 



perforated at or near the apex, or more or less slit at the froirl 

 margin. The hole or slit gives passage to a tubular orifice of the 

 mantle, through which excreta and water used for respiration 

 escape. The largest species are from California and South America. 



The Pleurotomariidae are extremely rare in recent times, only 

 six species being known, whereas over a thousand fossil forms 

 have been described. 



The ' Ear-shells' or c Ormers ' (Haliotidae) are found adhering 

 to rocks in most parts of the world, with the exception of South 

 America. Like the Limpets they hold on to the rocks with great 

 tenacity. The shells are lined with mother-of-pearl, and many 

 exhibit splendid colours and sculpture. The shell of Haliotis is 

 pierced by a series of holes parallel with the left margin ; through 

 these the animal protrudes slender tentacles. Haliotis tuberculata 



Fig. 14. 



Top-shell (Turbo petholatus). (From the Indo-Pacific Ocean.) 

 a. Inner surface of operculum ; b. exterior of ditto. 



is common on rocks and stones at low water in the Channel 

 Islands and the North of France, where it is frequently eaten ; 

 other species in New Zealand, China, Japan, West Africa, and 

 elsewhere, constitute a common article of diet. Haliotis shells 

 are largely used in the manufacture of pearl ornaments, and in 

 all kinds of inlaid work. 



The Trochidae and Turbinidae are two extensive families mainly 

 distinguished by the operculum, which is horny in the former, 

 and shelly in the latter. The shells of these molluscs are pearly 

 within, and are generally brightly coloured and highly ornamented. 

 Several very pretty species are found on our own shores. 



Of the Neritidae the species of Nerita are mostly found in 

 tropical countries, and like the Periwinkles have very strong 

 shells to resist the force of the breaking waves. Neritiria includes 

 both marine and freshwater species, which have less solid shells. 

 The shell of Septaria is shaped very much like those of Limpets, 

 except that the apex is at one end instead of central. 



