CLASSIFICATION 43 



in which the radula is wanting and the arms are 

 united by a membrane, while fins are developed on 

 the body. Some pelagic (Cirroteuthis) and deep-sea 

 forms (Opisthoteuthis) belong here, and possibly also 

 the fossil PalcEOctopus. (b) Trachyglossa, the 

 members of which have a radula, but no true fins. 

 The Common Octopus (Polypus vulgaris) and the 

 Argonaut are familiar examples of this tribe. 



Of the interrelationships of these five classes it 

 is impossible to say much in the present state of our 

 knowledge, beyond that the first four are the more 

 closely related. 



