862 PEOI". p. M. DUNCAN" OF THE EPITHECA 



physiological importance, and not to be of very satisfactory spe- 

 cific value on account of one well-known form having varieties 

 with and without this basal structure. It has been a perplexing 

 structure where it has been found so closely united to a wall of a 

 simple corallum as to render it impossible to determine whether 

 there is a wall at all, and whether the structure is not epithecate 

 entirely. Even in the days when the ' Hist. Nat. des CoralL' 

 was written, the secondary importance of the epitheca in classifi- 

 cation was evidently in the thoughts of Milne-Edwards and Jules 

 Haime ; and they decided, without the proper examination, that 

 in many instances where there was an epitheca on the base of a 

 compound Aporose coral, it must cover a common jDlateau or wall. 



Eeally it appears that epitheca may be a simply protective struc- 

 ture covering costge and the wall, and in the majority of such 

 instances preserving the coral from the attacks of parasites ; and 

 that it may also be of great physiological importance, replacing 

 the solid basal theca or wall in compound or colonial coralla, and 

 forming the foundation structure in others, whence the corallites 

 arise and grow upwards. 



I have chosen two examples of the importance of epitheca as a 

 fundamental basal structure. A species of Coeloria has no true 

 basal wall, but there is a mural epitheca. The mural defi- 

 ciencies of the species are also noticed between the series. 

 A species of Leptoria has also an epithecate basal wall. There is 

 also an example in a species of Fo7'ites of the method of growth 

 of expanded forms with wide bases, from the upper surface of an 

 epitheca. 



These instances, which are types of many others, indicate that 

 it is not reasonable to deny the classificatory value of the epitheca 

 entirely, and that it is of primary importance in many genera, 



A species of Forites and of Leptastrcea explain th.e importance 

 of the basal epitheca on the growth of incrusting corals. 



The importance of the epitheca is evident in Coeloria lahyrin- 

 thica, variety pacliychila, Ehrenberg. This species has been 

 called Coeloria Forshcelana by Milne-Edwards and Jules Haime ; 

 and it is well described in their Hist. Nat. des Corall. vol. ii. 

 p. 414. They only examined horizontal sections ; and they there- 

 fore missed the view of the curious internal construction of the 

 coral and the nature of the basal structures. 



In the generic diagnosis of Coeloria, Milne-Edwards and Jules 

 Haime noticed that the corallum is massive and cellular, very 



