2 BRITISH FOSSIL CORALS. 



The relation of the soft to the hard parts can then be well seen, and it will be at 

 once comprehended that there is a correspondence between the disc and the star-like 

 upper opening of the hard parts, which is called the calice} 



On examining a dried coral, or a Mell-preserved fossil specimen, certain plates will be 

 seen projecting inwards from the edge of the calice like the spokes of a wheel ; these are 

 the sejjta,^ and each is usually composed of two lamina, but their union is so exact that 

 it often requires microscopic sections for its determination. 



On the edge of the calice, and running down the outside of the coral, are some 

 projections, not so long as the septa, but corresponding generally with them, which are 

 called cosfce? 



The rim or edge of the calice, although it appears to be made up to a great extent by 

 the bases of the scjjta and costce, still presents a structure which unites their bases 

 laterally ; or, in other words, if the septa and costse were all planed off, there would remain 

 a more or less cup-shaped structure, called the theca or wall.'' 



The wall determines the shape of the coral ; and it may be even horizontal, or more 

 or less turbinate, cup-shaped, &c. The lowest part of the wall is called the base of the 

 coral, and it may be broad or pedunculated. 



The outside of the base, and more or less of the outside of the coral, are occasionally 

 covered by a calcareous investment, which results from a soft tissue, called by Dana 

 "foot-secretion.'' 



The inside of the base forms the floor of a cavity, whose superior termination is the 

 calice. This cavity is divided off by the septa, and its axis is usually filled up by a 

 structure called the coluinella^' which, in transverse sections of corals, occupies the 

 relative position of the axle to the spokes and tire of a wheel. The upper end of the 

 columella is free, and usually forms centrally the bottom of the calice. 



In some corals " there are thin processes, which are more or less oblique or even 

 horizontal in their direction ; they are situated between the sejjta, and they separate the 

 cavity into compartments, the upper or calicular lieing the newest. In other forms these 

 dissepiments {clissejnmenfa) are nearly vertical ; and in one great series they simply connect 

 the septa laterally, without dividing or restricting the cavity. These latter processes are 

 called synaplicalcB? Horizontal dissepiments are termed tabulae. 



There are corresponding processes between the costa; in many corals, and they are 

 often so fully developed as to project beyond and over them. The processes which are 

 inside the wall and between the septa compose the endotheca^ whilst those without the 

 wall and in relation to the costje are termed exotheca? 



The " foot-secretion " is an i'j)itheca}° 



1 Plate II, fig. 11. - Plate I, figs. 1, 3, 14, 18. '' Plate I, figs. 2, 7, 11. 



♦ Platel, figs. 3,4, 14, 13, 17, 18. ■• Plate I, figs. 5, (J, 8, 10, 12, 14, 18. « Plate I, figs. 15, 13, 18. 



■ 7 Plate III, figs. 1, 2. « Plate I, figs. 13, 15, 18. » Plate I, figs. 11, 18. 

 "' Plate I, fiz. IG. 



