THE ANTHOZOA 



Pro-Edwardsiae. 



Zoanthidea. 



Gonactinidae 



Oractidae." 



Monaulidae: 



Scleractiniae. 



Antipathidea. 

 Cerianthidea. 



Edwardsiidea. 



Sicyonidae. 



Polyopidae. 



Tealiidae, 



Whether or no the pro-Edwardsiae were developed from a 

 cruciform, i.e. a four-rayed ancestor, is a matter of conjecture. 

 The Rugosa, a heterogeneous group of Palaeozoic corals, are some- 

 times known as the Tetracoralla because of the characteristic 

 quadripartite symmetry which they exhibit. In such a form as 

 Stauria there are four principal septa, placed at right angles to 

 one another, and several secondary septa arranged in four systems, 

 those in each system inclining towards a primary septum. A 

 different arrangement of the secondary septa obtains in such forms 

 as Streptelasma, but the quadripartite symmetry is again con- 

 spicuous. It is tempting to suppose that the four principal septa 

 stood between four primary mesenteries, which were homologous 

 with the two pairs first developed in recent Zoantharia. This 

 would indicate a quadripartite ancestor for the Zoantharia, possibly 

 for all the Anthozoa. But in the present state of our knowledge 

 such inferences must be received with caution. The most that can 

 be said, is that microscopic examination of palaeozoic corals shows 

 that their skeletons are built up on the same plan as those of 

 recent corals, and that it may legitimately be inferred that the 

 correspondence in structure of the hard parts is evidence of a 

 correspondence in the structure of the soft tissues which gave rise 

 to them. The work of Pratz (104), von Koch (102), Quelch (86), 

 and Ogilvie (103) has resulted in -the breaking up of the old group 

 of the Rugosa, many members of which are now included amongst 

 families to which recent Scleractineae belong. 



The Zoantharia may be classified as follows : 



