APLYSIA. 197 



The Pleiirohranchiata are not all conchiferous, and of 

 such the generality have merely a thin horny shell, con- 

 cealed within the mantle, either on the back, or over the 

 breathing cavity. 



The order PletirohrancJdata is divided into tliree families : 

 — Aplysiana, Semiphyllidiana, and Bullacea. 



Family I. Aplysiana. 



Strange mimicry of forms, 

 Which earth reveals, and causing, in old times. 

 Men to shrink back with dread from near approach. 



In this small family the shells are concealed witliin the 

 fleshy substance of the mantle ; instead, however, of being 

 inserted on the back, they cover the breathing cavity, which 

 is situated on the right side only of the body. 



Two genera belong to this family — Aplasia and Bolahella. 



The Aplysia depilans of Linnseus, the type of this genus, 

 early attracted the attention of naturalists. His singular 

 resemblance to a crouching hare, increased still further by 

 the ear-shaped structure of the tentacula, gave rise to the 

 appellation of Sea-hare, both among the Greeks and Latins, 

 and by the former, especially, this strange creature was re- 



