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abdominal cavity. See V. I. p. 322. Note. (Copied from Miller's Crinoidea, P. 41. Pl. III.)

PLATE 51. V. I. p. 326, and 330.

Fig. 1. Pentacrinites Briareus, (nat. size) on a slab of Lias from Lyme Regis, covered with a large group of the same animals, in the collection of the Geological Society of London. (Original.)

Fig. 2. Rare and beautiful specimen of Briarean Pentacrinite, from the Lias at Lyme Regis, in the collection of Mr. Johnson, of Bristol, showing the plated integument of the abdominal cavity, terminated upwards by a flexible Proboscis, and surrounded by the commencement of the arms and fingers. This part of the animal is very seldom preserved. See V. I. p. 330. (Original.)

PLATE 52. V. I. p. 325.

Fig. 1. Recent Pentacrinus Caput Medusæ, from the bottom of the sea, near the I. Nevis, in the W. Indies, reduced from the Figure in Miller's Crinoidea, P. 48, Pl. I. In the front of this Figure, two of the arms with their hands and fingers are much smaller than the others, and show that these animals, when mutilated, have the power of reproducing lost parts.

D. Auxiliary side arms, articulating at distant intervals, with the vertebral column; these also, when mutilated, are reproduced.

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Miller's description of this recent Type, of a family of which a few individuals only have hitherto been found, affords examples of many very delicate and beautiful mechanical contrivances, which throw important light on corresponding parts of the fossil species of this, and of kindred genera that abound in strata of the Secondary series, and more especially in the Lias. (See V. I. pp. 325. 326. 328.)

Fig. 2. Pentacrinus Europæus, discovered in the Cove of Cork, and on other parts of the coasts of Ireland, by J. V. Thompson, Esq. (See V. I. p. 325.) In this figure several Individuals in different stages of developement, adhere by the base of an articulated column to the stem of a Coralline.

Fig. 2. One of the Individuals magnified and fully expanded. See V. I. p. 326.

Mr. J. V. Thompson has more recently conjectured that the Pentacrinus Europæus, which in early life is fixed by its stem to other bodies, is produced from the ovum of the Comatula, and becomes afterwards detached, and forms a perfect Comatula, capable of moving freely in the Ocean; at one time crawling amongst sub-marine Plants, at others floating, or swimming like Medusæ. (See Proceedings of Royal Society, London, June, 1835.)

Fig. 3. Small Briarean Pentacrinite, adhering to a fragment of Jet from the Lias at Lyme Regis. (See V. I. p. 329, Note.)

Fig. 4. Fragment of the column of Pentacrinites subangularis. The Vertebræ are nicely articulated to admit of flexure without risk of dislocation. The uppermost joint d. shows the lateral cavities for the articulation of auxiliary side arms. (Goldfuss. Pl. LII. f. g.)

Fig. 5. Vertical Section of Fig. 4. In this Fig. and in

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Fig. 4, the joints are of three degrees of magnitude; those at a. being the largest, those at c. the smallest and thinnest, and those at b. of an intermediate size. The edges of c. appear at the surface only upon the salient portion of the column, Fig. 4. (See V. I. p. 328, Note.)

Figs. 6, 7, 8, 9, 12, 13. Portions of the vertebral column of Pentacrinites basaltiformis. 6, 8, 12, show the stellated crenulations on the articulating facets of different parts of the column; 7, 9, show the tuber'cles on the exterior of each columnar joint, for the attachment of cortical contractile fibres. 13. d, shows the articulating facets of the auxiliary side arms. (Goldfuss.)

Fig. 10. Articulating facet of a columnar joint of Pentacrinites scalaris. (Goldfuss. Pl. LII. 3. h.)

Fig. 11. Fragment of a column of the same species. The joint d. bears sockets for the articulation of the side arms. The other joints have large tubercles for the attachment of cortical fibres. (Goldfuss, Pl. LII. 3. p.)

Figs. 14, 15, 16, 17. Articulating surfaces of joints in different parts of the column in Pentacrinites subangularis. The mechanism of each star seems differently disposed, to modify the amount of motion required at their respective places in the column. The tubercular surfaces between the rays or petals of the star indicate the action of the intervertebral contractile fibres. (Goldfuss, Pl. LII. 1. m. n. o. p.)

PLATE 53. V. I. p. 327, Note, et seq.

Fig. 1. 2. Upper parts of two nearly entire specimens of Briarean Pentacrinite, projecting in high relief from the surface of a slab, nearly two inches thick,

and entirely composed of a mass of petrified Ossicula of the same species of Pentacrinite. The surface of these fossils is covered with a delicate film of Iron Pyrites, which gives them the appearance of beautiful Bronze. (Original.)

1. Continuation of the stem of Fig. 1.

2o. Portion of the stem of Fig. 2.

F.

The length of these stems when entire, was three or four times that of the fragments here remaining.

Upon the stem 2a, nearly all the side arms retain their places in the grooves on each side of the salient angles of the pentagonal column; they diminish in size as they approach its upper extremity. This is also distinctly seen at the upper end of the column of Fig. 1.

First costal plate.

Second costal plate.

Fig. 3. Portion of a third column retaining nearly all its auxiliary side arms in their natural place.

Fig. 3. Continuation of the same column deprived of the side arms.

Fig. 4. Portion of another column, with traces of a few side arms rising from the lateral grooves.

Fig. 4. Continuation of Fig. 4.

Fig. 5. Fragment of another column, the joints of which

are so much bent without dislocation, as almost to give the column the appearance of a spiral disposi

tion.

Fig. 6. Body of a Briarean Pentacrinite and summit of its column, showing the interior of the ossicula that surround the abdominal cavity.

a

E. Pelvis. First costal Plate. From a specimen in the

F.

Oxford Museum. (Original.)

Fig. 7. Fragment of a column in the collection of Mr. J. Sowerby, showing the oblique articulation of the

base of the side arms, with the larger joints of the vertebral column. See V. I. p. 331. Note. (Original.) Fig. 8. Magnified Section of a portion of a column in the Oxford Museum. The joints, as in Pl. 52, Fig. 4, 5, and in Pl. 49, Figs. 3, 4, are alternately thicker and thinner; with a third, and still thinner joint interposed between them. See V. I. p. 327, Note. (Original.)

Fig. 8. Nat. size of Fig. 8.

Fig. 8. Portion of a Column, showing the manner in which the edges of the thinnest plates, c, are visible along the salient angles only. In the intermediate grooves the thicker plates, of the first and second sizes, a, b, overlap and conceal the edges of the thinnest plates, c. The principle of this mechanism is the same as in Pentacrinites subangularis, Pl. 52, Figs. 4, 5, and in Encrinites moniliformis, Pl. 49, Figs. 3, 4; but the circular form of the column in the latter, causes the smallest plate, c, to be visible around its entire circumference. See V. I. p. 327, Note. (Original.)

The bases of two side arms are seen in two of the grooves, articulating with the uppermost large joint of this column. On other large joints are seen the sockets from which similar side arms have fallen. Figs. 9, 10, 11, 12, 13. Various stellated forms on the articulating surfaces of Vertebræ, preserved in the dislocated mass beneath Figs. 1, 2. These petalshaped, and crenated rays were probably adapted to produce various degrees of flexibility, according to their respective places in the column. The small Vertebra on Fig. 13, is derived from another individual. (Original.)

The aperture at the centre of all these Vertebræ was for the passage of the alimentary canal, which

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