to various kinds of Sertularia and Flustracea in the Cove of Cork, and other parts of the coast of Ireland.

It appears that Pentacrinites are allied to the existing family of star-fishes, and approach most nearly to the Comatula; (See Miller's Crinoïdea, Pl. 1, and p. 127:) the bony skeleton constitutes by far the largest portion of these animals. In the living species this bony framework is invested with a gelatinous membrane, accompanied by a muscular system, regulating the movements of every bone. Although, in the fossil species, these softer parts have perished, yet an apparatus for muscular attachment exists on each individual bone.*

The calcareous joints which compose the fingers of the P. Europæus, together with their tentacula, are capable of contraction and expansion in every direction; at one time spreading outwards, like the Petals of an open flower (Pl. 52, Fig. 2,) and at another rolled inwards over the mouth, like an unexpanded bud; the office of these organs is to seize and convey to the mouth its destined food. Thus the habits of living animals illustrate the movements and manner of life of the numerous extinct fossil members of this great family, and afford an example of the validity of the mode of argument, to which we are obliged to have recourse in the consideration of extinct species of organic remains. In this process we argue backwards, and from the mechanical arrangements that pervade the solid portions of fossil skeletons, infer the nature and functions of the muscles by which motion was imparted to each bone.

I shall select from the many fossil species of the Genus Pentacrinite, that, which from the extraordinary number of auxiliary side-arms, placed along its column, has been called the Briarean Pentacrinite, and of which our figures (Pl. 51.

* See the tubercles and corrugations on the surfaces of the bones engraved at Pl. 52, Figs. 7, 9, 11, 13, 14, 15, 16, 17.

Figs. 1, 2; Pl. 52. Fig. 3.; and Pl. 53.) will give a more accurate idea than can be conveyed by verbal descriptions.*

Vertebral Column.

The upper part of the vertebral column of Pentacrinites is constructed on principles analogous to those already described in the upper part of the column, of the Encrinite.†

All the joints of the column, when seen transversely, present various modifications of pentagonal star-like forms; hence their name of Asteriæ, or star-stones.

These transverse surfaces are variously covered with a

* Pl. 51 represents a single specimen of Briarean Pentacrinite, which stands in high relief upon the surface of a slab of Lias, from Lyme Regis, almost entirely made up of a mass of other individuals of the same species. The arms and fingers are considerably expanded towards the position they would assume in searching for food. The side-arms remain attached to the upper portion only of the vertebral column.

At Pl. 53. Fig. 1 and 2 represent two other specimens of the same spe cies, rising in beautiful relief from a slab, which is composed of a congeries of fragments of similar individuals. The columns of these specimens, Fig. 2, a, show the side-arms rising in their natural position from the grooves between the angular projections of the Pentagonal stem. At Pl. 52, Fig. 1.

a b

F. F. are seen the costal plates surrounding the cavity of the body; at H the Scapula, with the arms and fingers proceeding from them to the extremi. ties of the tentacula.

At Pl. 53. Fig. 3. exhibits the side-arms rising from the lower part of a vertebral column, and entirely covering it. Fig. 4. is another column, on which, the side-arms being removed, we see the grooves wherein they arti culated with the alternate vertebræ. Fig. 5. exhibits a portion of another column slightly contorted.

The columnar joints of the Briarean Pentacrinite are disposed in pieces alternately thicker and thinner, with a third and still thinner joint interposed between every one of them. Pl. 53. Figs. 8, and 8a, a. b. c. The edges of this thinnest joint appear externally only at the angles of the column; internally they enlarge themselves into a kind of intervertebral collar, c.

C. C.

A similar alternation in joints of the Pentacrinites sub-angularis is represented in Pl, 52, Figs. 4 and 5,

succession of teeth, set at minute intervals from one another, and locking into the interstices between corresponding teeth on the surface of the next vertebræ, they are so disposed as to admit of flexure in all directions, without risk of dislocation.*

As the base or root of Pentacrinites was usually fixed to the bottom of the sea, or to some extraneous floating body, the flexibility of the jointed column, which forms the stem, was subservient to the double office, first, of varying, in every direction, the position of the body and arms in search of food, and secondly, of yielding, with facility, to the course of the current, or fury of the storm, swinging, like a vessel held by her cable, with equal ease in all directions around her moorings.

The Root of the Briarean Pentacrinite was probably slight, and capable of being withdrawn from its attachment. The absence of any large solid Secretions, like

* The ranges of tubercles upon the exterior surface of each joint in the fragments of columns, Pl. 52. Figs. 7. 9. 11. mark the origin and insertion of muscular fibres, by which the movement of every joint was regulated. At every articulation of the vertebræ, we see also the mode in which the crenated edges lock into one another, combining strength with flexibility. In Pl. 52, Figs. 11. and 13, the Vertebræ (d.) present five lateral surfaces of articulation, whereby the side-arms were attached to the vertebral column at distant intervals, as in the Pentacrinus Caput Meduse, Pl. 52. Fig. 1.

The double series of crenated surfaces, which pass from the centre to the points of each of the five radii of these star-shaped vertebræ, Pl. 62. Fig. 6. to 17.; and Pl. 53. Figs. 9. to 13, present a beautiful variety of arrangements, not only in each species, but in different parts of the column of the same species, according to the degree of flexion which each individual part required.

† Mr. Miller describes a recent specimen of Pentacrinus Caput Medusæ, as having the joints next to the base partially consolidated, and admitting but little motion, where little is required; but higher up, the joints become thinner, and are disposed alternately, a smaller and thinner joint succeeding a larger and thicker, to allow a greater freedom of motion, till near the apex this change is so conspicuous, that the small ones resemble thin leather-like interpositions. He also observed traces of

those of the Pear Encrinite, by which this Pentacrinite could have been fixed permanently to the bottom, and the farther fact of its being frequently found in contact with masses of drifted wood converted into jet (Pl. 52, Fig. 3.,) leads us to infer that the Briarean Pentacrinite was a locomotive animal, having the power of attaching itself temporarily either to extraneous floating bodies, or to rocks at the bottom of the sea, either by its side-arms, or by a moveable articulated small root.*

the action of contractile muscular fibres on the internal surfaces of each vertebra.

* The specimens of Briarean Pentacrinite at Pl. 52, Fig. 3. from the Lias at Lyme Regis, adheres laterally to a portion of imperfect jet, which forms part of a thin bed of Lignite, in the Lias marl, between Lyme and Charmouth.

Throughout nearly its whole extent, Miss Anning has constantly observed in this Lignite the following curious appearances: The lower surface only is covered by a stratum, entirely composed of Pentacrinites, and varying from one to three inches in thickness; they lie nearly in a horizontal posi. tion, with the foot-stalks uppermost, next to the lignite. The greater num ber of these Pentacrinites are preserved in such high perfection, that they must have been buried in the clay that now invests them before decomposition of their bodies had taken place. It is not uncommon to find large slabs several feet long, whose lower surface only presents the arms and fingers of these fossil animals, expanded like plants in a Hortus Siccus; whilst the upper surface exhibits only a congeries of stems in contact with the under surface of the lignite. The greater number of these stems are usually pa. rallel to one another, as if drifted in the same direction by the current in which they last floated.

The mode in which these animal remains are thus collected immediately beneath the Lignite, and never on its upper surface, seems to show that the creatures had attached themselves, in large groups, (like modern barnacles,) to the masses of floating wood, which, together with them, were suddenly buried in the mud, whose accumulation gave origin to the marl, wherein this curious compound stratum of animal and vegetable remains is imbedded. Fragments of petrified wood occur also in the Lias, having large groups of Mytili, in the position that is usually assumed by recent mytili, attached to floating wood,

28*

Side-Arms.

The Side-Arms become gradually smaller towards upper extremity of the column. In the P. Briareus (Pl. Fig. 3. and Pl. 53, Fig. 1. and 3.) these amount to nearl thousand in number.* The numerous side-arms of Briarean Pentacrinite, when expanded, would act as a iliary nets to retain the prey of the animal, and also se as hold-fasts to assist it in adhering to the bottom, or to traneous bodies. In agitated water they would close fold themselves along the column, in a position which wo expose the least possible surface to the element, and, toge with the column and arms, would yield to the direction the current.

* If we suppose the lower portion of the specimen, Pl. 53, Fig. to be united to the upper portion of the fractured stem, Fig. 3, we form a correct idea of the manner in which the column of this animal surrounded with this thousand side-arms, cach having from fifty to a dred joints, Pl. 53, Fig. 14. The number of joints in the side-a gradually diminishes towards the top of the vertebral column; but as of the lowest and largest (Pl. 53, Fig. 14.) contains more than a hund we shall be much below the reality in reckoning fifty as their aver number.

Each of these joints articulates with the adjacent joint, by proce resembling a mortice and tenon; and the form both of the articulating faces and of the bone itself, varies so as to give more universal mo as they advance towards the small extremity of the arm. See Pl. 53, 14. a. b.

In all this delicate mechanism which pervades every individual s arm, we see provision for the double purpose of attaching itself to extra ous bodies, and apprehending its prey. Five of these arms are set from cach of the largest joints of the vertebral column. At Pl. 53. 7. a. we see the bases, or first joints of these side-arms articulating w the larger vertebræ, and inclined alternately to the right and left, for purpose of occupying their position most advantageously for motion, w out interfering with each other, or with the flexure of the vertebral colum In the recent Pentacrinus Caput Medusa (Pl. 52, Fig. 1.) the side-a (D.) are dispersed at distant intervals along the column.