144 RAMBLES AND REVERIES. 



The great sub-kingdom of Coelenterata is divided 

 into Hydrozoa, of which the well-known Hyd/ra 

 may be taken as the type ; and Actinozoa, in which 

 corals are arranged. Actinozoa differ from Hydro- 

 zoa in the fact that while the body cavity of the 

 latter consists of one tube, that of the former is 

 divided into radial chambers. 



Actinozoa consist of the following four orders : 



(1) Zoantharia, sea-anemones and corals 



proper ; 



(2) Rugosa, an indefinite group, made up of 



extinct fossilised corals ; 



(3) Alcyonaria, in which are included the 



familiar dead-man's fingers or Alcyo- 

 nium, the so-called red coral, etc. ; 



(4) Ctenopkora, Venus' girdle, etc. 



Until recently corals were classified mainly by 

 means of their hard stony deposits, and were all 

 regarded as belonging to Zoantharia. This group 

 was sub-divided into 



(1) Tabulata, having horizontal partitions, 



which split them up into compartments, 

 as illustrated by Favosites Gothlandica 

 (Fig. 32, 33), where the polygonal tubes, 

 as well as the tabulae and perforations 

 connecting the tubes, are shown. 



(2) Rugosa, having radiating plates or septa 



in multiples of four, as seen in Litho- 

 strotion, an abundant carboniferous coral 

 (Fig. 34). 



