Fig. 23.
suggestive notice if the immense variety of fossil forms allied to those of the coral formations now progressing in the Pacific. The modern corals present to us a great diversity of structure, but they are excelled in all respects by those of the old world. The remains of these labours of insect life are exceedingly numerous; entire mountains are built, for the most part, with them; and the coral animals appear to have been as busy in the ocean which washed the cliffs of the Silurian boundary as it is at the present time on the reefs of Torres Straits and over the Indian Seas. [Fig. 24] and [25] represent the external appearance and the interior arrangement of the Calamopora polymorphus or Favosites, which is found at Combe Martin, Ilfracombe, and Plymouth. The arrangement of the tubes or cells, giving to the whole the character of some of the vegetable productions of the tropics, is very graceful.
Fig. 24. Fig. 25.
Fig. 26.
The Pleurodictyum problematicum ([Fig. 26]), from the ironstone bands on the banks of the Rhine, is singularly elegant. The disposition of the denticulated channels presenting the appearance of a delicate bead-like tracery, marking out a series of leaf-shaped divisions, gives great beauty to this variety. In the figure copied the Serpyllum curved in the centre adds too, rather than detracts from, the beauty of the fossil. Indeed, the manner in which Serpylla dispose themselves over many of the corals is singularly graceful and capable of many applications.