9 

 FAMILY I.— METRIDIAD^E. 



(No European species.) 



FAMILY II.— SAGARTIAD^E. 



I have thought fit to associate in this group those genera 

 of the Tribe, which have the following characters : — They 

 do not deposit a corallum. They have a broad base, capable, 

 at the pleasure of the animal, of firmly adhering to foreign 

 bodies, such as rocks, stones, and shells ; or of being used 

 as a foot, on which to creep, somewhat in the manner of a 

 snail. They have always simple, smooth tentacles, arranged 

 in (generally) uninterrupted circles at the margin of the 

 disk, but often encroaching far upon its surface. Their 

 body is for the most part pulpy or fleshy, generally lubri- 

 cated on the surface with copious mucus ; its exterior is 

 often studded with sucking cavities, Inch have the power 

 of adhering to foreign bodies, by the formation of a vacuum 

 within the cavity, its muscular edges being appressed by 

 the weight of the superincumbent atmosphere and water. 

 The margins of these cavities do not rise into conspicuous 

 warts when inactive. The integument is pierced with 

 loop-holes (cinclides), — special orifices, through which are 

 emitted and retracted fleshy cords (acontia), which have 

 their origin in the membranous partitions of the body- 

 cavity. These are filled with capsules (cnidce), which are 

 generally chambered, and which shoot a very short, but 

 densely-armed wire (ecthorceum). 



