REPORT ON THE ACTINIA RIA. 109 



as for example Halcampa clavus. We may gather from this how closely the Edwardsi* 

 are connected by transition forms with the other Actiniae, and how advisable it is to discuss 

 them along with the latter, and to separate them from the Alcyonaria. From this point 

 of view the constitution of the tentacles is of great importance, as they in no way resemble 

 the tentacles of the Alcyonaria. 



Tribe V. Zoanthe^. 



Actiniaria with numerous septa of two different kinds, smaller, imperfect, sterile micro- 

 septa, and larger perfect macrosepta furnished with reproductive organs and mesenteric 

 filaments ; the two kinds usually placed alternately, so that each pair is composed of a 

 larger and a smaller septum ; two pairs of directive septa at the ends of the sagittal axis, 

 one pair containing only macrosepta, the other only microsepta ; only one oesophageal 

 groove, corresponding to the larger directive septa ; animals usually forming colonies ; wall 

 usually traversed by ectodermal canals, and having the outside encrusted with foreign 

 bodies. 



Zoologists differ very much in their opinions as to the limits and the definition of 

 the Zoanthese. Milne-Edwards (Hist. des. CoralL, tom. i. p. 298) includes in this division 

 only colonial, sessUe forms which increase by basal gemmation and have a leather-like 

 sheath hardened by encrustation with sand granules (faux polypieroide) ; Gosse agrees 

 with him (Actinologia Britannica, p. 295), but considers the encrustation with sand 

 granules as a secondary character. Most zoologists keep to the definition given by 

 Milne-Edwards and Gosse. 



In 1856, Steenstrup described an Actinia under the name Sphenopus marsupialis, 

 which closely resembles the Zoanthese, but is distinguished from them by not form- 

 ing colonies and not being sessile. (Overs. Kongelige danske Videnskab. Selskabs 

 Forhand., p. 37, 1856). As Gray (Proc. Zool. Soc, p. 235, 1867) included this 

 Actinia among the Zoanthese, he set aside the characters used by Milne-Edwards, viz., 

 the formation of colonies and the sessile mode of life, but without replacing them in the 

 diagnosis by new characters, which would be at once common to all Zoanthese, and dis- 

 tinctive from other Actiniaria. To what degree the sharp limitation of the Zoantheee 

 suffered from this may be seen from the fact that Gray included in this tribe the genera 

 Edwardsia, Halcamj)a, &c. 



The discovery of Sphenopus led to difficulties as to the limitation of the Zoantheaj 

 which were also not obviated by the fact that Verrill considered Sphenopus to be related to 

 the Edwardsise, to which it has certainly a strong external resemblance. But anatomically 

 Sphenopus agrees so thoroughly wdth the Zoanthese that it cannot be separated from 

 them. A study of the arrangement of the septa is the only possible means of discover- 

 ing distinctive characters for the division. 



