110 MANUAL OF ZOOLOGY. 



1. Antipathidce. Sclerobasis spinulous or smooth ; tentacles 

 and soft parts in multiples of six. 



2. Hyalonemadce. Sclerobasis siliceous, composed of nume- 

 rous threads ; tentacles in multiples of five. 



3. Pennatulidce. Sclerobasis sulcate, free ; soft parts in 

 multiples of four. 



4. Gorgonidce. Sclerobasis sulcate, attached proximally: 

 soft parts in multiples of four. 



Sclerodermic coralla fall under two heads, according as they 

 are simply composed of scattered spicules, or are provided 

 with true thecce. 



I. Spicular coralla occur in the Zoantharia Malacodermata 

 (occasionally), and in the Alcyonidce ; and no differences can 

 be stated between the coralla themselves. The animals, how- 

 ever, differ entirely, the soft parts of the former being in 

 multiples of five or six, those of the latter being in multiples 

 of four. 



II. A thecal, sclerodermic corallum occurs in three distinct 

 sections of Actinozoa: 1. In the Zoantharia Sclerodermata. 

 2. In the Tubiporidce, amongst the Alcyonaria ; and 3. In the 

 Rugosa ; and the following are the distinctions between 

 them : 



1. Zoantharia Sclerodermata. Septa in multiples of five or 

 six, sometimes absent ; tabulse often present. 



2. Tuliporidm. Septa absent; thecse united externally by 

 distinct, horizontal ' epithecas.' 



3. Rugosa. Septa in multiples of four ; tabulse usually pre- 

 sent. 



CHAPTER XVI. 



CTENOPHORA. 



ORDER IV. CTENOPHORA. The Otenophora comprise ' trans- 

 parent, oceanic, gelatinous Actinozoa, swimming by means of 

 " ctenophores," or parallel rows of cilia disposed in comb-UJie 

 plates. No corallum. 1 (Greene.) 



The members of this order are all free-swimming organisms, 

 and they are placed by many amongst the Hydrozoa, from 

 which, however, they appear to be clearly separated by the 

 possession of a differentiated digestive sac. as well as by their 

 analogies with the Actinozoa, and their generally superior 

 degree of organisation. 



