4 BRITISH FOSSIL CORALS. 



tiulinally, and very short. It is bounded above by the Hps with their ridges,' below by 

 the pyloric constriction, and its outside is free in the visceral cavity. 



The ridges correspond with mesenteric folds, which are attached to the under surface 

 of the disc and to the outer or visceral surface of the stomach. Where the mesenteric folds 

 are attached to the lower margin of the stomach (the pyloric constriction), some tubular 

 prolongations" arise which float in the visceral cavity. There is an intimate relation 

 between the mesenteric folds, the septa, the interseptal loculi, and the tentacules. These 

 last open inferiorly into the visceral cavity between the mesenteric folds ; and, being hollow 

 and also perforated at their free extremity, they connect the visceral cavity with the 

 outside. The septa are developed between the mesenteric folds, and correspond with the 

 suhtentacidar spaces. 



There are, in some species, processes which are internal and accessory to certain septa ; 

 they arise from the base internally, and pass upwards in the form of thin plates, and are 

 attached to the columella. These are the pali.^ 



The costse and the exotheca are covered by, and, like all the other hard parts, are 

 developed by, soft tissues. 



The coloration of the soft tissues is very varied and Ijeautifid ; they are, of course, 

 not preserved in the fossil state, but they occasionally leave behind them the chemical 

 proofs of their former existence. 



The soft tissues are — 



1. The disc and its accessories. 



2. Membranes of the visceral cavity. 



3. Stomach. 



4. External membranes. 



The disc supports the tentacules and forms the lips. The external membrane coverino- 

 the co.staj arises from its external margin. It is marked by radiating ridges. 



The membranes of the visceral cavity line the interseptal loculi, and cover the septa, 

 wall, pali, and columella; they form also the mesenteiic folds and the tubular processes. 



The stomach, formed by membranes continuous above with those of the disc and below 

 with those of the visceral cavity, is bounded above by the mouth with its lips, which are 

 capable of being extended above the level of the disc. 



The foot-secretion or epitheca has its especial membrane. 



The membranes or tissues of these cavities of the disc and tentacules consist of three 

 layers. 



The Sclerenchjma, skeleton, or calcareous polypary — the hard parts, as they may be more 

 simply called — consist of the ii:all or Iheca, septa, costce, columella, pmli, endotheca, exotheca, 

 and epitheca. 



1 Plate II, figs. 11, 13. 2 Plate II, fig. 2. ^ Plate I, figs. 8, 9, 10, 1-1, 18. 



