THE CASSIS FAMILY. 



199 



is furrowed near the base. All these highly-enamelled Gasteropoda owe their beautiful polished 

 surfaces to the fact that the mantle lobes are so large as to meet over the back of the shell, and so 

 effectually protect it from all erosive action. The animal has a very large foot, in which the shell 

 is half buried. The eyes are placed near the tips of the tentacles. 



The Olives range from low water to twenty -five fathoms. All the species are very active ; they 

 may be seen gliding about near low water, or burying themselves in the sand as the tide retires. 

 They are animal feeders, and attach themselves to the baits on fishing-lines at the bottom. 



The Olives are all sub-tropical. One hundred and seventeen 

 species have been described. 



The genus Ancillaria resembles Oliva, both in its animal and its 

 shell. It is said by d'Orbigny to use its mantle lobes for swimming. 

 The shell has a larger spire than in Oliva, and the shell and spire are 

 entirely covered with shining enamel. 



In Ancillaria glabrata there is formed a sort of umbilicus between 

 the thickened inner lip and the body- whorl. The Ancillarias are all 

 sub-tropical shells. Twenty-three species are living. 



OLtVA ERY- 

 THKOSTOMA. 



FAMILY IV. CASSIDID^E. 



The shells of this family are very much inflated (ventricose) and 



somewhat globose ; the whorls are often ornamented with varices, or OLIVA POHPHYRIA. 

 ridges ; the aperture shows a re-curved canal in front ; the outer lip is thickened in most ; and the inner 

 lip is wrinkled or granular. The " Helmet shells " comprise many of the largest known Gasteropods. 

 They principally inhabit the warmer regions of the globe. 



Cassis has a thick tumid shell, with a very short spire, a long aperture, the outer lip bent 

 back and toothed, the inner lip being spread over the body-whorl ; the 

 canal is reflected in front. It has a small elongated operculum. 



Many of the shells of this species, as Cassis 

 rufa and the " Queen-Couch " (Cassis madagascar- 

 iensis), are employed in the manufacture of shell- 

 cameos. The best shell for cameo-engraving is the 

 Cassis rufa, from West Africa. The secret of 

 cameo-cutting consists simply in knowing that the 

 inner stratum of porcellanous shells is differently 

 coloured from the exterior. Cameos, in the British 

 Museum, carved on the shell of Cassis cornuta, are 

 white on an orange ground ; on Cassis tuberosa and 

 madagascariemis, white upon dark claret colour ; 

 on Cassis rufa, pale salmon colour on orange ; and 

 CASSIS CAXALICULATUS. on Strombus gigas, yellow on pink. 



Cassis inhabits shallow water. Thirty-four 



species are living in the tropical seas of to-day. A shell of the genus Cassis has been found in the 

 Pre-historic Cave-habitation of Les Eyzies, in Dordogne.* 



Dotium, or the " Tun," as this shell is sometimes called, has a large thin, light ventricose shell 

 with transverse ribs or furrows ; the spire is short, the aperture very large ; the canal is short and 

 reflected; the outer lip is crenated; it has no operculum. Fifteen species are met with in the 

 Mediterranean, India, China, the West Indies, Brazil, New Guinea, and the Pacific. 



The genus Cassidaria is found living in the Mediterranean. The shell is ventricose and tuber- 

 culated ; the aperture is narrow, ending in a produced and re-curved anterior canal ; the inner lip is 

 plicated, and spreads widely over the body-whorl ; the outer lip is reflected and crenated. 



In Triton the shell usually painted in all mythological pictures as being blown as a horn by sea- 

 deities attendant upon Neptune and Amphitrite the " periodic mouths," or rests, form alternating 



* See " Reliquiae Aquitanicae, " p. 179. 



CASSIS MADAGASCARIENSIS. 



