Fig. 5.
“The general principle,” remarks Dr. Buckland, “of dividing and subdividing the ribs, in order to multiply supports as the vault enlarges, is conducted nearly on the same plan, and for the same purpose, as the divisions and subdivisions of the ribs beneath the groin work in the flat vaulted roofs of the florid Gothic architecture.” In all these arrangements, and also in the bosses or tubercles, we have varieties giving both additional strength and beauty. A striking uniformity is found to prevail in even those shells of the Ammonites which seem the most complicated; and the elegance of their general appearance will be found to be due to the repetition, at regular intervals, of one symmetrical system of forms. In many of these fossil shells the pearly plates are dovetailed together in a curious and beautiful manner, the regular disposition of the sutures producing a very elegant foliated appearance. The charm of all these forms, and also of those fossil shells which are allied to the Ammonites, consists in the pleasing impression which is given by the gracefully curved outline, and the waving lines by which the shells are banded.
Fig. 6.
Among the Pectens—a class of shells common to the Sussex chalk—will also be found a great number of forms which, although not unlike many modern species, differ from them in some striking features, and which, independently of their novelty, are so very elegant that they seem peculiarly fitted for ornamental purposes. It has been with much difficulty that we have chosen two or three illustrations from this class, and we still feel doubtful if our selections exhibit the most favourable samples of their symmetry.
Fig. 7.