often forms a cluster of branches, two or three inches in circumference. The surface of the stems is covered with minute pores, and the cells are distinct, and placed in single rows on the margins; the left-hand figure of fig. 6 shows the plain surface, and that on the right, the opposite and inner, the margins being garnished with a row of cells; this structure is more distinctly shown in the fragment magnified, fig. 12.*

IDMONEA COMPTONIANA,† Lign. 64, fig, 14.This delicate coral is dichotomous, cylindrical, with elongated distinct cells, disposed in triplets, at regular distinct intervals, on one side of the stem,

With the exception of one specimen, to be noticed hereafter, we have now described all the Polyparia figured in Lign. 64; and have shown what interesting organisms may be detected in a few grains of calcareous earth. It would be easy to give restored figures of the beings whose stony skeletons are the subject of these remarks, from their close resem

* I have named this species to commemorate the researches of Frederic Dixon, Esq., of Worthing, who has formed an interesting collection of chalk fossils; and announced a work on the “Zoology of the Chalk Formation," to be richly illustrated with figures of many undescribed organic remains.

+ This specific name is in honour of the noble and highly respected President of the Royal Society, the Marquess of

Northampton.

blance to existing species; every pore and cell might be represented fraught with life; here the agile inmates, fully expanded, with their little arms, or tentacula, in rapid motion; there retreating within their recesses, and devouring the infinitesimal living atoms that constitute their food; or rapidly shrinking to the bottom of their cells upon the approach of danger; even their varied colours might be introduced, and thus a beautiful and highly interesting picture be presented to the eye, as now to the imagination.

Although, for convenience, I have selected the above examples principally from the cretaceous strata, the collector must not suppose that other formations are not equally prolific in these remains. The Coralrag of the Oolite, many beds of the Mountain limestone, and those of Dudley and Wenlock of the Silurian System, contain myriads of minute polypidoms associated with the coralline masses, of which those strata are so largely constituted. Exquisite figures of the Silurian corals are given, Murch. Sil. Syst. pl. 15, 16, and described by Mr. Lonsdale with characteristic accuracy. A slab of the Dudley limestone often has the entire surface studded with corals, shells, and crustaceous animals, of many species and genera, lying in bold relief, and in the most beautiful state of preservation.

VERTICILLIPORA, (Lign. 55.).—Cells poriform, arranged in meshes on the surface of convex

U

imbricating plates round a hollow axis, forming a fixed, irregular, subcylindrical polyparium. Lign. 55, fig. 4, represents with great accuracy a very extraordinary coral, common in the sand-pits of Faringdon, (Wond. p. 560, Tab. 105, fig. 3.) which is referred by Mr. Morris to this genus. * It is composed of short cylindrical anastomosing branches, or tubes, emanating from an expanded base, divided internally by transverse parallel plates, covered with exceedingly minute pores, or cells, disposed in meshes; the plates enclose a hollow pillar or axis. This structure is well shown in the figure.

LUNULITES (Lign. 55.).-Polyparium orbicular, convex above, concave below; concavity radiated ; convexity covered with cells, arranged in concentric circles on diverging radii. A species of this coral is often found in the chalk. Lign. 55, fig. 1, represents a specimen from the South Downs.

GRAPTOLITHUS (Lign. 65.).—Polyparium elongated, undivided, sublinear, acuminated or obtuse, serrated.

These curious bodies abound in some of the Silurian strata, and may be considered as belonging to the characteristic fossils of those ancient deposits. They are the horny central axes, or supports, of zoophytes supposed to be related to the Pennatula,

* Catalogue of Brit. Foss. p. 46.

or sea-pen,* and are always more or less flattened from compression.

In a recent state these bodies were probably covered with a soft, or albuminous mass, studded

with polype-cells, disposed in rows along the margins of the lateral, curved, grapple-like processes, as in the zoophytes termed Virgularia,t to which they bear a greater analogy than to Pennatula. It has

* See British Zoophytes, p. 174, fig. 22.

+ Ludensis, from Ludlow-to indicate the habitat of the fossils.

See British Zoophytes, Pl. XXIV.

been suggested by some eminent naturalists, that the originals were more nearly related to Sertularia, but they appear to me to present close affinity to the family of Pennatulida. If two specimens of the Graptolithus Ludensis be placed together, so that the elongated smooth edges be in apposition, the united stems will be seen to offer a general resemblance to the axis of Virgularia mirabilis.

The species fig. 2, occurs in the lower Silurian rocks, and volcanic grits.* Graptolites have been found in strata of the same age in Norway, Sweden (Ly. II. p. 173.), and Scotland. I have received slates literally covered with them, from the Cambrian rocks of the United States, by Benjamin Silliman, jun. Esq.

The distinguished author of the Silurian System remarks, that the nature of the strata in which these remains occur in Radnorshire, indicates a condition of the sea well suited to the habits of the family of Sea-pens; for the recent species live in mud and slimy sediment, and the fossils are imbedded in a finely levigated mud-stone, which, from its structure, must have been tranquilly deposited. There are six or seven species of Graptolites, all belonging to the most ancient fossiliferous deposits.

I shall next describe some of the single lamellated corals, and then notice those which consist of an

*Murch. Sil. Syst. p. 694.