INTRODUCTION. 19 
Epitheca.'—This structure is’ occasionally seen both in simple and in compound 
corals ; it is the ‘‘ foot-secretion ” of Dana,? and may either be closely applied to the wall 
of the corallite or may simply cover the coste, leaving them more or less perfect in their 
ornamentation. In some simple corals it covers the wall so closely as to resemble a 
coating of varnish, in others its texture is rough and marked with concentric or encircling 
ridges, and in a few instances it is marked by chevron-shaped lines. ‘The epitheca may 
be very thin or very dense, and it may simply cover the base or only reach a short 
distance upwards from it ; or it may cover all the external surface as far as the calicular 
margin. The dense epitheca of some Montlivaltie is accompanied by a great diminution 
in the strength of the wall; this is seen also in many fugose corals. ‘The epitheca of 
compound corals is rarely ornamented, but is laminate and often readily destroyed. Its 
preservation in fossils is comparatively rare, and it should therefore not be made of very 
great classificatory value. 
The epitheca developes processes in certain species and only covers the base of others ; 
it is porcellanous in some, as in Fladellum, and pellicular in others, as in Balanophyllia. 
It is membranous, striated, verrucose, marked by growth-rings, shining, rough and partial, 
in different species. 
It is a structure evidently formed after the development of the costz, and results from 
a tissue which is a continuation of that which determines the agglutination of the bases 
and peduncles of certain corals to their supporting earth, stone or rock, or foreign 
organism. 
IIl.—Anatomy or THE Sort TissvuEs. 
The membranous surface which covers the calice, supports the tentacules, and is 
perforated by the mouth, is called the Zentaculiferous Disc.’ 
The opening of the mouth is central, and is either circular or elliptical in outline ; it 
is at the top of a truncated cone* whose base is continuous with the disc and whose 
height varies according to circumstances. The margin of the opening—the lip—is usually 
marked by radiating ridges, is very prehensile, and can be moved in different directions. 
The cone, whose upper extremity is the mouth, varies in its power of protrusion in 
different species; this is especially great when the tentacules are small and are only 
arranged at the margin of the disc ; and, as a rule, when the tentacular development is 
considerable the labial protrusion is slight. In some species, such as Heliastrea cavernosa 
and Lithophyllia Cubensis, there is a considerable space between the mouth and the 
tentacules, and these last are feebly developed; consequently the mouth can be so pro- 
truded as to form a hollow between its cone and the base of the tentacules. 
1 Plate I, fig. 16. 2 Plate IV, fig: 6. 
Plate Uy figa?4, 9-11 *t0 S135 ity 16; 17 4 Plate II, figs. 10, 11. 
