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up of many similar parts disposed like Rays around a common centre.
Mr. Agassiz has recently shown, (London and Edin. Phil. Mag. Nov. 1834, p. 369,) that they do not partake of this character, from which the division of radiated animals is named; but that their rays are dissimilar, and not always connected with a uniform centre; and that a bilateral symmetry, analogous to that of the more perfect classes of animals, exists throughout the families of Echini, Asteriasc, and Crinoidea.
ECHINIDANS AND STELLERIDANS.
The History of the fossil species of Echinidans and Stelleridans has been most beautifully illustrated, in the plates of the Petrefacten of Prof. Goldfuss. Though derived from Strata of various degrees of high antiquity, they are for the most part referred by him to existing Genera.
The family of Echinidans appears to have extended through all formations, from the Epoch of the Transition series to the present time.*
No fossil Stelleridans have yet been noticed in strata more ancient than the Muschelkalk.
As the structure of the fossil species of both these families is so nearly identical with that of existing Echini, and Starfishes, I shall confine my observations respecting fossil animals in the class of Echinoderms to a family which is of rare occurrence, excepting in a fossil state, and which seems to have prevailed most abundantly in the most ancient fossiliferous formations.
• I found many years ago fossil Echinidans in the Carboniferous limestone of Ireland, near Donegal, they are however rare in the Transition formation, become more frequent in the Muschelkalk and Lias, and abound throughout the Oolitic and Cretaceous formations.
Among the fossil families of the Radiated division of animals, the Geologist discovers one whose living analogues are seldom seen, and whose vast numerical extent and extraordinary beauty entitle it to peculiar consideration.
Successions of strata, each many feet in thickness, and many miles in extent, are often half made up of the calcareous skeletons of Encrinites. The Entrochal Marble of Derbyshire, and the Black rock in the cliffs of Carboniferous limestone near Bristol, are well known examples of strata thus composed; and show how largely the bodies of Animals have occasionally contributed by their remains, to swell the Volume of materials that now compose the mineral world.
The fossil remains of this order have been long known by the name of Stone Lilies, or Encrinites, and have lately been classed under a separate order by the name of Crinoidea.
This order comprehends many Genera and numerous Species, and is ranged by Cuvier after the Asteriae, in the division of Zoophytes. Nearly all the species appear to have been attached to the bottom of the Sea, or to floating extraneous bodies.*
* These animals form the subject of an elaborate and excellent work, by Mr. Miller, entitled a Natural History of the Crinoidea, or Lily-shaped Animals. The representations at PI. 48, and PI. 49, Fig. 1. of one of the most characteristic species of this family, being that to which the name of sionelily was first applied; and the figures of two other species at PI. 47, Fig. 1, 2, 5, will exemply the following definition given of them by Mr. Miller. "An animal with a round, oval, or angular column, composed of numerous articulating joints, supporting at its summit, a series of plates, or joints, which form a cup-like body, containing the viscera, from whose upper rim proceed five articulated arms, dividing into tentaculated fingers, more or less numerous, surrounding the aperture of the mouth, (PI. 47. Figs. 6, x. 7, x) situated in the centre of a plated integument, which extends over the abdominal cavity, and is capable of being contracted into a conical or proboscal shape."
The two most remarkable Genera of this family have been long knowd to Naturalists by the name of Encrinite and Pentacrinite; the former (see PI. 49, Fig. 1, and PI. 47, Figs. 1. 2. 5.) most nearly resembling the external form of a Lily, placed on a circular stem; the latter (see PI. 51, and PI. 52, Fig. 1, 3,) retaining the general analogies of structure presented by the Encrinite, but, from the pentagonal form of its stem, denominated Pentacrinite. A third Genus, called A-piocrinites, or Pear Encrinite, (PI. 47. Figs. 1, 2.) exhibits, on a larger scale, the component parts of bodies of this family; and has been placed by Mr. Miller at the head of his valuable work on the CrinoVdea, from which many of the following descriptions and illustrations will be collected.
Two existing species of recent animals throw much light on the nature of these fossil remains; viz. the Pentacrinus Caput Medusae from the West Indies, represented at PI. 52, Fig. 1. and the Comatula fimbriata,* figured in the first plate of Miller's Crinoidea.
We will proceed to consider the mechanical provisions in the structure of two or three of the most important fossil species of this family, viewed in relation to their office as Zoophytes, destined to find their nourishment by spreading their nets and moving their bodies through a limited space, from a fixed position at the bottom of the sea; or by employing the same instruments, either when floating singly through the water, or attached, like the modern Pentelasmis anatifera, to floating pieces of wood.
Although the representatives of CrinoVdeans in our modern seas of rare occurrence, this family was of vast numerical importance among the earliest inhabitants of the ancient deep.* The extensive range which it formerly occupied among the earliest inhabitants of our Planet, may be estimated from the fact, that the CrinoYdeans already discovered have been arranged in four divisions, comprising nine genera, most of them containing several species, and each individual exhibiting, in every one of its many thousand component little bones,f a mechanism which shows them all to have formed parts of a well-contrived and delicate mechanical instrument; every part acting in due connexion with the rest, and all adjusted to each other with a view to the perfect performance of some peculiar function in the economy of each individual.
* The Comatula presents a conformity of structure with that of the Pentacrinite, almost perfect in every essential part, excepting that the column is cither wanting, or at least reduced to a single plate. Peron states that the Comatula suspends itself by its side-arms from fuci, and Polyparies, and in this position watches for its prey, and attains it by its spreading arms and fingers. Miller, p. 182.
The joints, or little bones, of which the skeletons of all these animals were composed, resemble those of the starfish: their use, like that of the bony skeleton in vertebral animals, was to constitute the solid support of the whole body, to protect the viscera, and to form the foundation of a system of contractile fibres pervading the gelatinous integument with which all parts of the animal were invested.}.
The bony portions formed the great bulk of the animalas they do in star-fishes. The calcareous matter of these little bones was probably secreted by a Periosteum, which in cases of accident, to which bodies so delicately constructed must have been much exposed in an element so stormy as the sea, seems to have had the power of depositing fresh matter to repair casual injuries. Mr. Miller's work abounds with examples of reparations of this kind in various fossil species of CrinoVdeans. Our PI. 47, Fig, 2, a. represents a reparation near the upper portion of the stem of Apiocrinites Rotundus.
* The monograph of Mr. Miller, exhibiting the minute details of every variation in the structure of each component part in the several Genera of the family of Crinoidea, affords an admirable exemplification of the regularity, with which the same fundamental type is rigidly maintained through all the varied modifications that constitute its numerous extinct genera and species.
t These so-called Ossicula are not true bones, but partake of the nature of the shelly Plates of Echini, and the calcareous joints of Starfishes.
t As the contractile fibres of radiated animals are not set together in the same complex manner as the true muscles of the higher orders of animals, the term Muscle, in its strict acceptation, cannot with accuracy be applied to Crinoideans; but, as most writers have designated by this term the more simple contractile fibres which move their little bones, it will be convenient to retain it in our descriptions of these animals.
In the recent Pentacrinus (PI. 52, Fig. 1,) one of the arms is under the process of being reproduced, as Crabs and Lobsters reproduce their lost claws and legs, and many lizards their tails and feet. The arms of star-fishes also, when broken off, are in the same manner reproduced.
From these examples we see that the power of reproduction has been always strongest in the lowest orders of animals, and that the application of remedial forces has ever been duly proportioned to the liability to injury, resulting from the habits and condition of the creatures in which these forces are most powerfully developed.
As the best mode of explaining the general economy of the Crinoidea, will be to examine in some detail the anatomy of a single species, I shall select, for this purpose, that' which has formed the type of the order, viz. the Encrinites moniliformis (see PI. 48, 49, 50.) Minute and full descriptions are given by Parkinson and Miller of this fossil, showing it to combine in its various organs a union of mechanical contrivances, which adapt each part to its peculiar functions in a manner infinitely surpassing the most perfect contrivances of human mechanism.
Mr. Parkinson* states that after a careful examination he has ascertained that, independently of the number of pieces.
* Organic Rermins, vol. ii, p. 180,