388 THE SPINED NER1TINA. 



A VEEY curious elongated shell occupies the centre of the engraving. This is the 

 shell probably known by the name of WEAVER'S SHUTTLE on account of its peculiar 

 shape. It is, in fact, one of the Eggs, but has the aperture lengthened into a long canal 

 at either end. The foot of this species is narrower than in the other members of the 

 same genus, but is especially adapted for crawling over the stems of the gorgonia, one of 

 the zoophytes on which the mollusc feeds. 



OUR third and last example of these shells is the WARTY EGG, remarkable, not so 

 much for the tuberculated exterior of the shell, as for the richly spotted foot and mantle. 



WE now arrive at a vast army of shells called the Sea Snails, and distinguished 

 by having the edges of the aperture without notches, the shell spiral or limpet-shaped, 

 and the operculum either horny or covered with hard, smooth, shelly matter. 



OUR first example of this family is the NATICA, the large shell in the centre of the 

 engraving. 



As will be seen, on reference to the illustration, the mantle of this species is very 

 large, and the front of the foot is developed into a fold, which turns backward over the 

 head and serves as a kind of protection. As the animal is without eyes, this curious 

 structure causes no inconvenience. All the Naticae, of which about ninety species are 

 known, are found upon the sandy beds of the sea, and sometimes are taken at a depth of 

 nearly six hundred feet from the surface. They are very predaceous in their habits, 

 feeding principally on little bivalves, which they can assault with their short but strongly 

 armed tongue-ribbon. The eggs of these creatures are very remarkable. They are 

 compacted into a kind of spiral roll, broad and rather short, which is suffered to be 

 flung about at the mercy of the waves, and is sometimes found resting on the sands when 

 the tide has retreated. 



The colours of the Naticse are marvellously permanent, and even in the fossil state 

 they are preserved and retain some degree of their original brilliancy. The species which 

 is here represented is yellowish, and marked with grey bands. 



AN empty shell may be seen lying in the right-hand corner of the engraving. This 

 is the NATICELLA-SHELL, closely allied to the preceding, and given in order to exhibit the 

 shape of the aperture. 



JUST above the naticella may be seen a shell, together with the animal, represented as 

 crawling. 



This is an example of another family, the ISTeritidae, and is popularly known by the 

 name of the SMOOTH NERITA. As may be seen on reference to the engraving, the foot is 

 moderate, the tentacles are exceedingly large, and the eyes are set on footstalks just 

 behind the base of these organs. The Neritas are all inhabitants of the warmer seas, and 

 are found plentifully within the tropics. 



The colour of the present species is slightly variable, but in the individual specimen 

 the shell is marked with bold zigzag streaks of white and pale buff, and the interior is 

 pure white at the lip, changing to beautiful canary yellow in the interior. The operculum 

 is thick, hard, solid, and highly burnished, as if overlaid with glass ; its edge is regularly 

 and finely grooved. 



SEVERAL allied shells are inhabitants of the fresh instead of the salt waters, and are 

 known as Neritines. 



One of the most curious of these shells is the SPINED NERITINA, which may be seen 

 on the extreme left of the illustration. The animal of the Neritina is not unlike that of the 

 preceding genus, but there are one or two minute differences which cannot readily 

 be explained without figures. The operculum is shelly, with a flexible border, and has 

 some small teeth on its straight edge. All the Neritinse are globular in their general 

 shape, darkly spotted or banded with black and purple, and covered with a polished 



