Fig. 10. A polished slice of a beautiful marble richly marked by the sections of the enclosed corals (_Astrea undulata_, of Dr. Fleming); from Switzerland: probably from the Oolitic or Jurassic formation. Fig. 11. Vertical section of a fossil coral, showing the transverse arrangement of the internal cells. Figs. 12 & 13. These specimens are polished sections of a very beautiful compound coral (_Astrea Tisburiensis_, of Miss Benett), which occurs in a silicified state in the Portland beds that are quarried at Tisbury, in Wiltshire. Masses of chert (a kind of coarse silex or flint), wholly made up of this coral, are often met with, and when sliced and polished are extremely beautiful and interesting; the originally calcareous fabric of the zoophytes being perfectly transmuted into silex, and the interstices filled up with a similar substance, but of a different colour.[28] [Footnote 28: Specimens of the Tisbury Astrea, and of most if not all of the coralline marbles figured and described, may be obtained of Professor Tennant; and also vases, &c. of the various marbles of Derbyshire.] [Illustration: Plate XXXIX.] PLATE XXXIX. Various Fossil Corals and Sponges, or Amorphozoa. Fig. 1. A coral from the Dudley limestone. (_Favosites?_) Fig. 2, is a vertical section of figs. 4 and 5, to show the internal arrangement of the cells. Fig. 3. The under surface of a very common species (_Favosites Gothlandica_, of Goldfuss); from the Wenlock limestone of Dudley. A magnified view of part of the surface, to show the honeycomb structure, is given in fig. 7. Fig. 4, the under, and fig. 5, the upper surface, of a small coral (_Cyclolites ?_) from the Oolite. Fig. 6. A silicified branched sponge, (_Spongites lobatus_, of Dr. Fleming,) from the chalk of Berkshire. Fig. 9, is a beautiful silicified, lobate, spongoid body, (_Siphonia_,) probably from the greensand. Siliceous cruciform spicula obtained from this fossil are represented in fig. 8. Zoophytes of this kind, like many of the sponges, have their tissues strengthened by, and largely composed of spicula, which vary in form and size in the different species and genera. Many sponges and Siphoniæ in flint, and in the chert of the greensand, consist almost entirely of spicula, which may be easily detected by a slightly magnifying power. Fig. 10. Another common Dudley Coral. (_Porites pyriformis_, of Mr. Lonsdale.) Fig. 11. A beautiful coral (_Explanaria flexuosa_, of Dr. Fleming), from the Coral Rag of Steeple Ashton, Wilts. The outline indicates the mode of increase, according to Mr. Parkinson, of this form of zoophyte.