The origin of these fossils will be understood by reference to the four specimens delineated in [Lign. 81]. In fig. 3, a fungiform flint, resembling fig. 6, of [Lign. 80], is seen in the lower part of a cup-shaped zoophyte; while above, and surrounding the flint, the impression remains of the reticulated outer surface, deeply coloured by a ferruginous tinge. In fig. 4, [Lign. 81], a small turbinated flint, resembling fig. 4, of [Lign. 80], occupies the base, and three rootlets are seen emerging from it at a. In [Lign. 82, fig. 1], in which the chalk has been removed so as to expose the outer surface of the Ventriculite, a flint occupies the centre at c; above which, the radiating reticulated structure is spread out on the chalk, a; the base, with its roots, is shown at b.
Lign. 81. Ventriculites radiatus; 1/6 nat.
Chalk; near Lewes.
| Fig. | 1.— | A perfect specimen in chalk, inverted, showing the external reticulated surface; the apex of the base projects in the centre. |
| 2.— | Specimen expanded, displaying the inner surface, studded over with the openings of the cells or tubes. | |
| 3.— | A Ventriculite in chalk; the lower part inclosed in flint. | |
| 4.— | Portion of a Ventriculite; the stem towards the base is enveloped in flint, and three radicle processes spread from it into the surrounding chalk at a. |
These specimens demonstrate that all the flints referred to, have been moulded in the cavities of cyathiform zoophytes; and that their diversity of figure has arisen from the amount of silex that happened to permeate the organism; if but a small proportion of silica in solution was present, then flints, like fig. 4, were produced; if the quantity were sufficient to fill up a considerable part of the tissues of the original, fungiform flints, as [Lign. 80, fig. 3], and [Lign. 81, fig. 3], were the result. The disciform flints originated from the expanded examples, [Lign. 81], figs. 1 and 2: and when the silex was insufficient to silicify the entire zoophyte, an annular flint, resembling a quoit, was formed.
Lign. 82. Portions of Ventriculites; 1/4 nat.
Chalk, near Lewes.
| Fig. | 1.— | A specimen, in which the middle is inclosed in a flint c; the external structure of the Ventriculite is seen at a, expanded on the chalk; and the pedicle with its roots is exposed at b. The figures are one-fourth the size of the originals. |
| 2, 3, | 5.—Chalk specimens, showing the external structure of stems of Ventriculites. | |
| 4.— | A siliceous cast of the cavity of a Ventriculite covered with papillæ, moulded in the orifices of the cells. |