38o COELENTERATA ANTHOZOA chap. 



arrangement in larger groups have presented many difficulties, 

 and have led to considerable differences of opinion ; and even now, 

 although our anatomical knowledge has been greatly extended, 

 the classification cannot be regarded as resting on a very firm 

 basis. The families may be grouped into two sub-orders : — 



Sub-Order 1. Actiniina. — The tentacles are simple and 

 similar, and there is one tentacle corresponding to each inter- 

 mesenteric chamber (endocoel). 



Sub-Order 2. Stichodactylina. — The tentacles are simple 

 and similar, or provided with teat-like or ramified pinnules. One 

 or more tentacles may correspond with an endocoel, and there 

 may be two kinds of tentacles (marginal and accessory) in the 

 same genus. 



Sub-Order 1. Actiniina. 



Fam. 1. Halcampidae. — This family is clearly most closely 

 related to the Edwardsiidea. There are, however, twelve complete 

 mesenteries of the first cycle, and a second cycle of more or less 

 incomplete mesenteries. The tentacles are usually twelve in 

 number, but may be twenty or twenty-four. There is no pedal 

 disc, but the base is swollen and rounded or pointed at the end. 



The genus Halcampa includes a considerable number of small 

 species occurring in the shallow waters of the temperate northern 

 hemisphere, and of the Kerguelen Islands in the south. Three 

 British species have been described, of which Halcampa chrysan- 

 thellum alone is common. The larva with eight tentacles and 

 eight mesenteries has been found living on the Medusa 

 Thaumantias. 



Peachia is a genus containing Anemones of much larger size 

 (10-25 cm.). It is remarkable for the very large siphonoglyph 

 on the ventral side of the stomodaeum, prolonged into a 

 papillate lip projecting from the mouth called the " conchula." 

 The genera Scytophoms from 150 fathoms off Kerguelen and 

 Gyractis from Ceylon, although showing some remarkable 

 peculiarities of their mesenteric system, appear to be closely 

 related to this family. 



Ilyanthus mitchellii is a large Anemone with a vesicular 

 base, forty-eight tentacles and mesenteries, occurring in the 

 English Channel, but it is not very common. It is usually 



