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 well-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 septa,’ and each is usually composed of two Jamineg, 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 costa. 
The rim or edge of the calice, although it appears to be made up to a great extent by 
the bases of the septa and coste, still presents a structure which unites their bases 
laterally ; or, in other words, if the septa and coste were all planed off, there would remain 
a more or less cup-shaped structure, called the ¢heea 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 dase 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 1s divided off by the septa, and its axis is usually filled up by a 
structure called the columella,’ 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 septa, and they separate the 
cavity into compartments, the upper or calicular being the newest. In other forms these 
_ dissepiments (dissepimenta) 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 synapticule.’ Horizontal dissepiments are termed tadule. 
There are corresponding processes between the costs im 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 eudotheca,* whilst those without the 
wall and in relation to the coste are termed evotheca.* 
The ‘ foot-secretion”’ is an epitheca.” 
1 Plate II, fig. 11. 2 Plate I, figs. 1, 3, 14, 18. 3 Plate I, fies. 2,7, a1. 
4 Plate I, figs. 3,4, 14,15, 17, 18. 5 Plate I, figs. 5, 6, 8,10, 12, 14, 18. 6 Plate I, figs. 15, 13, 18. 
7 Plate III, figs. 1, 2. 8 Plate I, figs. 13, 15, 18. 9 Plate I, figs. 11, 18. 
10 Plate I, fig. 16. 
