THE BLACK OLIVE. 381 



JUST below the needle-shell is seen the beautiful SPOTTED IVORY-SHELL, also a native 

 of the hotter latitudes. 



Few species, not more than eight or nine in number, are known to exist at the present 

 day. They are all very smooth and polished on the exterior, and their substance is so thick 

 and solid that they seem almost to be made of earthenware. They reside at a moderate 

 depth, being generally found in twelve or fourteen fathoms of water. It is worthy of 

 notice that the rich spotted markings of the shell are repeated upon the body of the 

 animal. The members of this genus possess tolerably large eyes, set at the base of the 

 long tentacles. As in the preceding genus, the operculum has its nucleus at the 

 pointed end. 



The colour of the Spotted Ivory-shell is pure porcelain- white, richly spotted with deep 

 brownish red, something like the tint known to artists as burnt sienna. It is not a very 

 large shell, being about two inches in length. 



THE last figure, which occupies the extreme left of the illustration, represents the 

 APPLE TUN-SHELL, one of a moderately strong genus, deriving their popular name from 

 the rounded and barrel-shaped outlines of the shell. 



The animal is shown as it appears when crawling, for the purpose of exhibiting the 

 curious striped edges of the feet, and the manner in which the siphon is carried bent over 

 the front of the shell like the uplifted proboscis of an elephant. In these shells the spire 

 is comparatively small and short, and the aperture very large, thus producing a great 

 contrast to the needle-shell on the same engraving. About fourteen species of Tun-shells 

 are known, all inhabiting the warmer seas. 



The colour of the Apple Tun-shell is nearly white, diversified here and there with a 

 few spots of the palest saffron. The interior, however, is much more deeply coloured than 

 the outside, being of a rich yellow with a slight dash of orange. 



THE beautiful HELMET-SHELLS also belong to this useful family. Several of these 

 shells are employed by the engravers in the manufacture of cameos, the differently 

 coloured layers producing most exquisite effects when cut by a judicious operator. The 

 colours vary greatly in the different species, and sometimes there is a slight variation even 

 in different individuals belonging to the same species. Cameos, for example, that are cut 

 from the HOBNED HELMET-SHELL (Cassis cornuta) are white, upon a ground of rich 

 orange ; those that are made from the WAKTV HELMET-SHELL (Cassis tuberosa) are white, 

 on deep dark red ; the cameos formed from the shell of the EUDUY HELMET (Cassis rufa] 

 are saffron-yellow on warm orange. Another beautiful species, called the QUEEN CONCH 

 (Cassis Madagascar iensis), furnishes a white cameo on a claret-coloured ground. 



These shells are tolerably thick and solid, and their external surface is covered with 

 bold ridges, marking the periodical growth. These ridges are technically called " varices." 

 All the Helme1>-shells are natives of the tropical seas, and appear to prefer the shallow 

 waters near the coast. 



ON the extreme left of the next illustration is a dark smooth shell, represented 

 as crawling on the ground, and partially enveloped in the spotted textures of the 

 living creature. 



This is the BLACK OLIVE, so called on account of the jetty blackness of its exterior, 

 and the oval, rounded form, which is not unlike that of the fruit whose name it bears. 

 The genus Oliva is a very large one, comprising more than one hundred species, and found 

 in all the warm and tropical seas. As may be seen by the figure, the mantle is furnished 

 with two large lobes, that nearly meet over the back while the animal is moving, and 

 which throw out certain filamentary projections, that look very like tentacles in the wrong 

 place. The foot is very large so large, indeed, that the shell is partly buried in its soft 

 material and the eyes are, as may be seen in the figure, placed before the middle of the 

 tentacles. 



Owing, probably, to the great development of the foot and mantle, the Olives are active 

 creatures, gliding about with tolerable speed, burying themselves in the sand when the 



