628 



Haddon and Shackleton — A Revision of the British Actinice. 



We acknowledge only one family in the group which we divide into two 

 sub-families, the Brachycneminae, and the Macrocneminse, which are based upon 

 the two well-known types of mesenterial arrangement. It is worthy of notice that, 

 so far as our knowledge at present extends, the Macrocneminae alone are repre- 

 sented in the North Atlantic, although they are world-wide in distribution. 



The following Table shows the chief generic distinctions at a glance, and 

 demonstrates that the group is a very homogeneous one. We regard Parazoanthus 

 as being the least specialised genus on account of its having a single endoderinal 

 sphincter muscle, and Zoanthus as the most specialised, as it possesses a double 

 mesogloeal sphincter muscle. We omit Mammillifera, as the type species have 

 never been described from an anatomical point of view : — 



