served, but it displays the centre filled with numerous parallel openings, the sections of longitudinal tubes, which are surrounded by a broad zone of spongeous tissue. Among the chalk flints the collector will find numerous specimens, whose forms depend on the enclosed sponges, and other related Amorphozoa. Some are of a large size, and of a globular or spherical shape; others are irregularly branched, the surface presenting the usual white calcareo-siliceous coating of the flint nodules, and feeling rough to the touch; and, wherever an opening or fracture appears, indications of the porous texture will be discovered. This class of fossils is at present so imperfectly investigated, that names can be assigned but to few of the common examples, and these would afford no guide to the collector, without the aid of numerous figures, which our space will not permit.* Porifera of the same genera, if not species, as those above described, exist also in some of the secondary strata below the chalk. CHOANITES.-Form various, generally spherical, funnel-shaped, or globular, with a central opening in the upper part; the original substance carneous, or gelatinous, and capable of imbibition and contraction: base fixed. * Several kinds are represented in the Geology of Sussex, Tab. XV. The fossils which I have placed under this genus,* are closely related to a recent zoophyte (Alcyonium LIGN. 58. CHOANITES KÖNIGI. (G. A. M.) Chalk, Lewes. 5. Various kinds of SPICULA of fossil sponges X X. ficus of Linnæus), which is described as having the * See Foss. South D. p. 178. form of a fig, with the upper part flattened, and possessing a central cavity; the lower and smaller end fixed by root-like processes. It is of a rich brown colour, and its substance, when dried, appears like that of nut-galls.* There are several species of Choanites in the chalk formation, but the most remarkable is that figured in the annexed lignograph 58, and which may be considered as the type of the genus. This zoophyte frequently occurs in the semi-diaphonous pebbles on the Sussex coast, and gives rise to such beautiful and varied markings, that polished sections are mounted for brooches and other ornaments, being termed by the lapidaries, petrified sea-animal flowers.† Among the shingle on the shore at Bognor, Worthing, and other places, very fine examples may be obtained. Lign. 58, fig. 4, represents the usual appearance of a siliceous Choanite. Fig. 2. is the upper part of a Choanite preserved in chalk, and richly coloured by iron; the opening at the summit a, is the orifice of the central cylindrical cavity, which is filled up by chalk; and in flint specimens, with silex of a different colour to that of the surrounding mass. fig. 2. were placed on the top of fig. 4, the general shape of the zoophyte would be represented. The opening at the base of fig. 4, marks the spot from If † A coloured vertical section is figured in "Thoughts on a Pebble," Pl. 2. 1 J THE MEDALS OF CREATION. CHAP. VIII. which root-like processes of attachment proceeded. The vertical section of a flint, similar to fig. 4, is shown at fig. 3; and in this example are seen the central cavity, and a section of the substance of the zoophyte, which is traversed by numerous tubes, that commence in the opening, on the inner wall of the central cavity, or digestive sac, and ramify in the mass of which the body was composed. A transverse section of a similar flint is delineated in fig. 1; the central spot indicates the sac filled with white flint, and tubes or canals are seen radiating from it through the substance of the zoophyte; a powerful lens shows the interstitial structure to be granular. From the perfect transparency of the body when silicified, and the rich tints it has acquired from metallic solutions, and the compressed state in which it is often found, it seems probable that the original was composed of a soft, glutinous substance, like the Actiniæ, strengthened by spicula ; for numerous tri-radiate spines, like those on the left hand of fig. 5, Lign. 58, occur occasionally in chalk specimens.* A smaller species, of a subrotund form (C. subrotundus), that occurs in groups of three or four (Foss. South D. Tab. XV. fig. 2.), is not uncommon in * Miss E. Benett was one of the earliest investigators of these interesting fossils, and my attention was first directed to the subject by specimens from her choice collection; for this species is abundant in the Wiltshire chalk. the chalk of Sussex and Wiltshire; and is often found associated with a turbinated zoophyte, apparently of the same genus (Lign. 60, fig. 1.). The latter has a shallow central cavity, with a broad smooth margin, a reticulated external surface, and radicle processes proceeding from the base. CHOANITES FLEXUOSUS (Lign. 60, fig. 10.) is cyathiform, and has the margin of the central cavity marked with flexuous indentations (Foss. South D. Tab. XV. fig. 1.). PARAMOUDRA.-This vernacular Irish term was introduced by Dr. Buckland, in his account of some gigantic flints, thus popularly named, that occur in the chalk near Belfast, and also at Whitlingham, near Norwich. These fossils are of an irregular, oblong, spherical, or pyriform shape, having a cavity above, which, in some specimens, extends to the bottom; at the base indications of a pedicle, or process of attachment, are seen; in short, they closely resemble, upon a large scale, some of the funnel-shaped sponges, so frequent in the flints of the South Downs. Their general appearance is represented Lign. 59, from Dr. Buckland's illustrations: b. is a single specimen, partly imbedded in the chalk, and c, d. two of the fossils in contact, the pedicle of the upper lying in the cavity of the lower; but this position appears to be accidental. They are from one to two feet or more in length, |