16 BRITISH FOSSIL CORALS. 



with them. It will be noticed that in some species of Cyalhophyllidce, and in many 

 Tertiary^ simple corals, that the external edges of the septa correspond with the intervals 

 between the costae, and not with those organs themselves. This is not an accidental 

 variation in growth, but is constant in several species. 



In some species there are small costae which do not correspond to any septa ; the 

 large costae are continuous with septa ; but these so-called rudimentary costae simply 

 project externally, and correspond internally with an interseptal space.^ 



In some corals the epitheca, whilst covering the costae and hiding them from view, 

 appears to have produced their partial absorption, for above the limit of the epithecal 

 structures the costae may be seen to be prominent and to be greatly ornamented.^ It 

 may be inferred that in young specimens whose epitheca is not fully developed the costae 

 would command more attention in the specific diagnosis than is proper, and this has 

 taken place in more than one instance. The costae may, however, retain all their orna- 

 mentation when covered by a very dense and membranifonn epitheca, and this peculiarity 

 is generally constant. Occasionally the long spines on the costae of some Lithophi/llace<s 

 project through the epitheca, but in the majority of instances they are included. It is 

 evident that the costae were well developed before they were covered by the epitheca. 



The more prominent the costae, the more they are exposed to the destructive influences 

 of rolling and of wear and tear ; it happens, therefore, that the large cristaeform costae, the 

 long delicate spines on their edges, and the finely granulated dentations, are rarely dis- 

 tinguishable in many fossil species, and their former existence can only be suggested in 

 consequence of scars and raggedness on the surface, or by the preservation of an ornament 

 here and there. 



In examining the costal structures the specimen should be placed in several 

 positions and in different lights, for small structural peculiarities are often hidden in the 

 shadows. 



Endotheca. — The structure which, stretching from one septum to another, closes more 

 or less the interseptal loculi,''' — the horizontal processes which, extending from side to 

 side in a corallite, shut out all beneath from communication with above,^ and certain 

 exaggerated septal papillae, which meet in the interlocular spaces and form a system of 

 joistwork,* constitute the Endothecal Sderenchyma. 



The first variety, termed by Milne-Edwards and Haime " Traverses '' or Endothecal 

 dissepiments^ characterises many genera ; whilst the second, termed by these authors 

 " Planchers " or Tahulm^ serves to distinguish a great series of Madrejjoraria. The third 

 variety is seen in the family Func/idcB, which it characterises, and the name Synapticula 

 is given to it. 



1 'Ann. Mag. Nat. Hist.,' loc. cit. ^ i^ Turbinolia Forbesi, Dune. ' Plate I, fig. 16. 



* Plate I, figs. 16, 18 ; Plate IV, figs. 2, 4, 6, 8. 5 pja^g m^ flg §_ g^ iq, 1 1. 



6 Plate HI, figs. !, 2. 7 Plate V, fig. 3 ; Plate I, figs. 15, 18. ^ Plate I, figs. 3, 5, 14. 



