INTRODUCTION. 33 



There is a vast difference between the economy of a coral with imperforate and a 

 coral with porose walls, and a method of diagnosis arises from it. The aporose and 

 perforate sections are at once natural and easily distinguished. 



The horizontal tabulae may be found in perforate as well as in aporose corals, but the 

 absence of vesicular endotheca and of the usual endothecal arrangements may be so marked 

 that a section can be very fairly marked off. Nevertheless, the gradation of dissepiments 

 into horizontal tabulae^ is witnessed in many Mugosa, and is not feebly marked even in 

 some corals of the section Aporosa. 



The tubulate wall and defective septa offer materials for a doubtful section, for they 

 are very closely matched by some aporose forms. 



The Bugosci^ are so peculiar in their septal arrangement that, as a rule, they are dis- 

 tinguished at once ; but their diagnosis will be carefully elaborated in a future page; 



When the section of a coral has been determined, the existence or deficiency of endo- 

 thecal structures becomes diagnostic. The existence of endotheca refers very definitely 

 to the nutrition and growth of the species, and is readily discoverable. 



The method of multiplication, the existence of fissiparous or serial calices, and the 

 independence or the soldered condition of the corallites, must be then noticed. 



The existence of pali and the nature of the septal arrangement must be made out, 

 and the absence or presence of a columella determined. The nature of the columella, 

 the shape of the calices, the size and ornamentation of the septa and costse, must be 

 examined, and the plain or incised condition of the septal margin decided. The exist- 

 ence of exotheca, coenenchyma, peritheca, and epitheca is to be discovered, and the pecu- 

 liarities of the structures noticed. The height and breadth, and the habit of the coral 

 should be estimated. There are, then, many data for the foundation of a classification ; 

 and the following tables have been drawn up of that of the genera which are most likely 

 to be found in the British Secondary and Tertiary rocks.^ 



1 Plate IV, fig. 2. "' Plate III, figs. 15, 18, 19, 20. 



^ The tables have been selected from the 'Hist. Nat. des Coral,,' Milne-Edwards and Jules Haime, and 

 have been altered -where requisite. 



