HELMET-SHELLS. 



211 



is used as money by the Africans : hundreds of tons are imported to Liverpool 

 and exported for barter.* 



The Harp-Shells (Harpri) are recognizable by the prominent ribs upon 

 their surface, the last of which forms the marginal border. These shells are very 

 beautiful. The animal (Fig. 217) is furnished with a large foot, broad in front, 

 and pointed posteriorly ; its tentacles are provided with eyes situated near 



their bases ; it has no operculum. 



FIG. 220. CASSIS TUBEROSA. 



FIG. 221. THORNY WOODCOCK. 



The Helmet-Shells (Cassis) are of an oval shape, and have their opening 

 long and narrow. The large and massive shells of some species are used for 

 the manufacture of cameos, which are cut out of their thick substance, as repre- 

 sented in the accompanying figure (Fig. 220). The subject is worked in relievo 

 in the white portion or outer table of the shell, while the inner layer, generally 

 of a pink or reddish-brown tint, is left for the background. 



The Rock-Shells (Mnrex) are ornamented with spines, rough tubercles, or 

 leafy, frilled processes, arranged in a regular but peculiar order. The species 

 which we have figured (Murex tennispimi) is common in cabinets, and known 

 to collectors by the name of the " Thorny Woodcock." 



* From a coarse comparison of the cowrie-shells to a pig's back, they were vulgarly 

 known to the Portuguese as Porcellane (Porcellus, a little pig). When the beautiful 

 ware known as china was first imported, the resemblance of its glaze to the enamel of 

 the cowrie-shell caused it to be called "porcelain." 



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