628 



Haddon and Shackleton — A Revision of the British Actiniw. 



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

 sub-families, the Brachycneminse, 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 endodermal 

 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 : — 



Genus. 



Mesenterial aiTange- 

 ment. 



Sphincter. 



Gonads. 



Body-wall and Coenenchyme. 



Zoanthus. 



Brachycnemic. 



Double mesogloeal. 



c? or J , 2 

 + 



Unincrusted; well-deve- 

 loped ectodermal canal 

 , system. 



Isaurus. 



Brachycnemic. 



Single mesogloeal. 



(? or J^, 2 



+ 



Unincrusted ; ectodermal 

 and endodermal bays 

 and small canals ; some- 

 times solitary. 



Gemmaria. 



Brachycnemic. 



Single mesogloeal. 



(?, ? 



( Incrusted ; lacunae ; often 

 1 solitary, always attached. 



Palytboa. 



Brachycnemic. 



Single mesogloeal. 



^, ? 



Similar to above, but 



polyps immersed in 



\ expanded coenenchyme. 



Sphenopus. 



Brachycnemic. 



Single mesogloeal. 



? 



(Incrusted; cell-islets; al- 

 I ways solitary and free. 



Epizoanthus. 



Macrocnemic. 



Single mesogloeal. 



<y, 2 



Incrusted ; cell-islets. 



Parazoanthus. 



Macrocnemic. 



Endodermal. 



<?, $ 



Incrusted ; ectodermal 

 canals ; cell-islets ; en- 

 circling sinus ; ectoderm 

 always contmuous. 



