16 BRITISH FOSSIL CORALS. 
with them. It will be noticed that in some species of Cyathophyllide, and in many 
‘Tertiary’ simple corals, that the external edges of the septa correspond with the intervals 
between the costz, 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 costee which do not correspond to any septa; the 
large coste are contmuous with septa; but these so-called rudimentary coste simply 
project externally, and correspond internally with an interseptal space.” 
In some corals the epitheca, whilst covering the costz and hiding them from view, 
appears to have produced their partial absorption, for above the limit of the epithecal 
structures the costa 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 cost 
would command more attention in the specific diagnosis than is proper, and this has 
taken place in more than one instance. The coste may, however, retain all their orna- 
mentation when covered by a very dense and membraniform epitheca, and this peculiarity 
is generally constant. Occasionally the long spines on the costa of some Lithophyllacee 
project through the epitheca, but in the majority of instances they are included. It is 
evident that the coste were well developed before they were covered by the epitheca. 
The more prominent the coste, the more they are exposed to the destructive influences 
of rolling and of wear and tear; it happens, therefore, that the large cristeeform coste, 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,s—the horizontal processes which, extending from side to 
side in a corallite, shut out all beneath from communication with above,’ and certain 
exaggerated septal papillz, which meet in the interlocular spaces and form a system of 
joistwork,° constitute the Hndothecal Sclerenchyma. 
The first variety, termed by Milne-Edwards and Haime “ Zraverses” or Endothecal 
dissepiments,’ characterises many genera; whilst the second, termed by these authors 
“ Planchers” or Tabule,' serves to distinguish a great series of Madreporaria. The third 
variety is seen in the family Pungide, which it characterises, and the name Synapticula 
is given to it. 
1 ¢Ann. Mag. Nat. Hist.,’ loc. cit. 2 In Turbinolia Forbest, Dune. 3 Plate I, fig. 16. 
4 Plate I, figs. 16, 18; Plate IV, figs. 2, 4, 6, 8. 5 Plate III, fig. 8, 9, 10, 11. 
6 Plate III, figs. ‘1, 2. 7 Plate V, fig. 3; Plate I, figs. 15, 18. 8 Plate I, figs. 3, 5, 14. 
