MOLLUSC A. 273 



aiice of a broad, flat, opaque, white slug, with the dorsal 

 disc divided into four lobes. The two side lobes of the 

 disc are the edges of the mantle turned up ; the front lobe 

 covers the head, and the back lobe hides from view a very 

 beautiful broad, white, transparent shell, known more gene- 

 rally by the name of Bidlaa aperta. 



Sepiola vulgaris. 



The Cuttle-fish tribe, being more oceanic than littoral, 

 do not thrive well in confinement. They will not live 

 many days in a tank, but while they do live their habits 

 are not uninteresting. Of course the larger species are too 

 cumbersome for the purpose, but the smaller ones have 

 often been preserved in confinement long enough for obser- 

 vations on their habits. In some respects they approach 

 the Eadiate groups of animals ; having the mouth central, 

 on the top of the head, and the organs of prehension and 

 locomotion, arms or legs, placed in a circle around it. In 

 other respects they incline towards the vertebrate groups ; 

 some of them being provided with an internal bone or pen, 

 which may be considered a rudimentary vertebral column. 

 Others are furnished with a shell. The soft bone sold in 

 shops for birds to nibble at belongs to Sejoia officinalis ; 



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