Lign. 88. Fossil Corals.
Upper Silurian, Dudley.[244]

Fig.1.—Astrea ananas.
1a.—A polished slice of Marble, formed of Astrea pentagona.
Devonian. Torquay.
2.—Syringopora ramulosa. Mt. L. Derbyshire.
3.—A Fragment of Favosites Gothlandica. Ohio. (By Dr. Owen.)
4.—Anthophyllum Atlanticum. Cret. U. States. (By Dr. Morton.)
5.—Caryophyllia annularis. Oolite. Faringdon.

[244] Figured in Pict. Atlas, pl. xxxvii. fig. 1.

ASTREA.

Astrea. [Lign. 88, figs. 1, 1a.]—Polyparium massive, irregular in shape, generally globular, formed by an aggregation of lamellated, radiated, shallow, polymorphous cells.

The corals of this genus are very numerous in the seas of the Tropics, and there are many species in the Oolite, and older secondary formations. The Astreæ, Caryophylliæ, Cyathophylla, &c., form the principal mass of the coralline limestones of the Oolite, termed the Coral-rag, from the abundance of these relics: being literally composed of an aggregation of large corals, the interstices of which are filled with shells, radiaria, &c., either whole, or in a comminuted state. The heaps of this limestone placed by the road-side, in the N. W. of Berkshire, appear like fragments of an old coral-reef, and attract the notice even of the most incurious observer. I have figured a specimen of Astrea, [Lign. 88], fig. 1, and a polished section, fig. 1a, from Clifton, a locality well known for the stupendous mural precipices of mountain limestone rocks, which yield beautiful examples of coralline marble.[245] The mode of increase of the Astrea is very curious; a subdivision takes place in the old cells, after the manner of the Infusoria; and among the fossils, a star or cell may often be seen in progress of division into two, three, or four stars (Sil. Syst. pl. xvi. fig. 6). A living polype of this genus is figured, Wond. pl. vi. fig. 13.

[245]

Astrea arachnoides, Pict. Atlas, pl. xxxviii. fig. 4.
——— undulata, ibid, pl. xxxviii. fig. 10.
——— Tisburiensis ibid. pl. xxxviii. figs. 12, 13.

A species of Astrea (A. Tisburiensis. Wond. p. 641, fig. 9), is found in large hemispherical masses, completely silicified, at Tisbury, in Wiltshire. The transverse surface displays, in some specimens, beautiful white radiated stars, on a dark blue ground; and in others, the colours of the stars and ground are reversed. This silicified coral is obtained from a bed of chert, a foot in thickness, which is interstratified with the Portland limestone, this division of the Oolite being quarried around Tisbury.[246]