228 SHELLS AND MOLLUSCOUS ANIMALS. 



spreading portion, and is often mistaken for that 

 of some species of whelk. Even in a later stage 

 of progress, it is again very dissimilar to the fully 

 formed shell, and we might pick up three specimens 

 so differently formed, as that an inexperienced 

 conch ologist would deem each to be of a different 

 species. Some of the foreign kinds of Strombus 

 are very large and handsome shells, and some 

 species are known to have produced pearls. 



Another common univalve may be easily de- 

 scribed. This is the Tooth-shell (Dentalium entalis), 

 which is just like a little horn in shape, hollow, 

 slightly curved, open at both ends, about an inch 

 and a half long, and of a white or yellowish 

 colour. Its polished surface is sometimes marked 

 with rings of yellow or brown. It is found on 

 sandy shores, placed in a perpendicular position in 

 the sand or mud. Some species of the Tooth- 

 shell are found in the seas of almost all countries. 

 The animal which inhabits this shell is of a conical 

 form, with an elongated fleshy foot. It has beau- 

 tiful thread-like tentacula on the back of its neck, 

 which are its breathing organs, and serve to en- 

 tangle its prey. 



But we must pass on to another order of Mol- 

 lusca, the cuttle-fish tribe, Cephalopoda, which 

 exhibit a far higher order of organization than the 

 animals of any other division of this large class. In 

 these only are to be found the rudiments of aix 

 internal skeleton. There is a skull containing the 

 brain, distinct organs of hearing and smelling, and 

 eyes very superior in structure to that of any other 

 of the mollusca. The term Cephalopoda signifies 

 head-footed, the feet of the animal being placed 

 round the head. These feet are of great strength, 



