20 BRITISH FOSSIL CORALS. 
The ridges which mark the lips are continued on to this vacant space, and radiate 
towards the bases of the tentacules. 
In some species the moveable mouth and the hollow between it and the tentacules are 
of more use in obtaining food than the tentacules themselves.’ 
The contrary is very evident in Caryophyllia clavus’ (the Caryophyliia borealis of British 
zoophytologists), and in Cladocora cespitosa.* In these species the tentacules are greatly 
developed and extend close up to the base of the cone which is surmounted by the mouth 
and lips; there is but little of the disc unoccupied, and the power of protrusion on the 
part of the cone is comparatively slight. Yet it must be observed that when the tentacules 
are withdrawn, the mouth is capable of being projected further than when they are in full 
extension. 
The lips, the external surface of the cone, and the disc, are covered with cilia. At the 
marginal extremity of the disc in some species, and scattered over more or less of the 
whole disc and extending even very close to the labial orifice, in others, are the tentacules.* 
These organs vary in length and thickness in different species, but each has a base con- 
tinuous with the tissues of the disc and opening into the upper part of the visceral cavity. 
Generally terminated by a bulbous swelling, the tentacules are perforated throughout by a 
delicate canal, and consist of tissues which render them very mobile, contractile, extensile, 
and more or less prehensile. The external margin of the disc corresponds with the 
calicular margin ; it is separated from it by a very small space, is continuous with the 
tissues covering the outside of the coral, and in some species has a small fold which 
covers in the tentacules. 
The opening of the mouth, when fully expanded, admits of the columellary surface 
being seen at the bottom of a shallow cavity ; and the sides of this cavity, marked by the 
continuation of the ridges noticed on the lips and disc, are often protruded through 
the lips.» The cavity is the stomach, and it is separated from the visceral cavity, which 
is below or at about the level of a prominent columella, by a faint constriction—the 
pylorus. ‘The stomach is very short and very extensile. 
‘The sides of the cavity are continuous, by means of the lips, with the outside of 
the disc; they are formed by the same tissues, but the tegumentary layer of the 
disc is altered and becomes the superficial layer of the mucous membrane of the 
stomach. 
The ridges already noticed on the lips, disc, and stomach, correspond on the under 
side of the disc and outside of the stomach with mesenteric folds. 
The pylorus opens into the visceral cavity, whose upper boundary is the lower surface 
of the tentaculiferous disc, and it therefore is clear that the stomachal membranes con- 
! Plate II, fig. 10. 2 Plate II, figs. 7—11. 3 Plate II, fig. 4. 
4 Plate 1; figsnds 72 15,12, 13; 14,907,186, 19520. 
* The ridges are seen in Plate II, figs. 11, 13, 14. 
