CHAPTER IX.

[278]Mr. Miller's work should be consulted for details of structure.

This Encrinite when lying in relief on the rock, with its receptacle entirely or partially closed (seeWond.p. 548), so strikingly resembles the bud or expanding flower of a Lily or Tulip, as to justify the popular name of Stone-lily. An exquisite specimen is figured by Mr. Parkinson;[279]the British Museum possesses some fine examples.[280]

[279]Pict. Atlas, pl. xlviii.[280]Petrifactions, p. 77.

[279]Pict. Atlas, pl. xlviii.

[280]Petrifactions, p. 77.

Mr. Parkinson detected the animal membrane in ossicles of this crinoid, by immersing them in dilute hydrochloric acid.[281]My friend Mr. Frederick Harford has repeated the experiment with success.

[281]See Pict. Atlas, pl. xlvii.fig.47.

PENTACRINITES.

Pentacrinites.—The description of the recentPentacrinuscaput-medusæ(ante,p. 282.), illustrates the characters of the crinoideans whose fossil remains are so familiar to the palæontologist, under the name of Pentacrinites. In these animals the pieces composing the receptacle are firmly articulated together; the rays of the disk are fixed immediately to the summit of the column by special ossicula; and the stem is composed of angular pieces, which are generally pentagonal. The receptacle is small, and situated deep between the bases of the arms; it is closed above by an integument covered by minute plates or flat ossicles (Lign.94,fig.2). The fossil remains of several species are abundant in the Lias and Oolite of Dorsetshire, Somersetshire, &c. Slabs of limestone may be extracted with the surface covered with these crinoideans, spread out as if floating in their native element; very commonly they are transmuted into sulphuret of iron, or have a coating of brilliant pyrites.[282]The neighbourhoods of Lyme Regis, and Charmouth, are celebrated for these organic remains. A small specimen of the arms of a pentacrinite on Lias shale is figured inLign.94,fig.3.

[282]Pictorial Atlas, pl. li. lii.

The arms in many of the plumose pentacrinites are very long and thickly beset with side-arms, and minute pinnæ, all of which are composed of separate articulated ossicles, so that the number of bones in a single endo-skeleton of those crinoids amounts to from fifty to one hundred and fifty thousand distinct pieces. The Briarean Pentacrinite,[283]so named from its numerous tentacula, is literally a tuft of articulated processes, appearing like a delicate fibrous plume attached to a stem. ThePentacrinus Hiemeriis a beautiful example of this type of crinoids, of which there is a noble group, comprising upwards of thirty individuals, on a slabin the British Museum,[284]exposed on the surface of the stone in as perfect a state as if just dredged up from the bottom of the sea. The pentacrinites are for the most part entire; the peduncle being fixed, and the column extending upwards in gentle undulations, and supporting the receptacle, from which the arms are gracefully outspread in various attitudes. The structure of the receptacle, and of the arms, and the extreme delicacy of the finer tentacula made up of countless minute ossicula, are admirably shown in this unique and most instructive fossil.

[283]Pictorial Atlas, pl. xlvii. The Briarean Pentacrinite is fully illustrated and described in detail in Dr. Buckland's Bridge water Essay, p. 484.[284]This species was named and figured by M. König in his "Icones Fossilium sectiles," pl. iii.fig.29, in 1826. See Petrifactions, p. 88.

[283]Pictorial Atlas, pl. xlvii. The Briarean Pentacrinite is fully illustrated and described in detail in Dr. Buckland's Bridge water Essay, p. 484.

[284]This species was named and figured by M. König in his "Icones Fossilium sectiles," pl. iii.fig.29, in 1826. See Petrifactions, p. 88.

Lign. 94. Actinocrinites, or Nave Encrinites.Fig.1.—Actinocrinus Parkinsoni.(Org. Rem.ii. pl. xvii.Pict.Atlas, pl. li.)2.—Section of anActinocrinus, (Miller's Crinoideæ, pl. ii.)a. Proboscideal protrusion of the plate and integument.b. Sections of the folded or closed arms.3.—Arms of a Pentacrinite, on Lias-shale;Lyme Regis.

ACTINOCRINUS. CYATHOCRINUS.

Actinocrinus(Nave Encrinite).Lign.94,fig.1, 2.(Wond.p. 585.Bd.pl. xlvii.)—The column is formed of numerous round ossicula, possesses side-arms, and is fixed by root-like processes. The receptacle is of an irregular subspherical form, the arms passing off at right angles like the spokes from the nave of a wheel; hence the name. The base is composed of three plates which support five hexagonals and one pentagonal, and on these are three other series; from the upper margin of the last, five arms are given off. The receptacle is closed by a dome-shaped tesselated covering (Lign.94,fig.2), having on one side the opening for the mouth and vent. The specimen,fig.1, is a receptacle without a stem, and with but a few joints of the arms; this is the usual state in which these fossils are obtained.Fig.2 is anActinocrinitein which part of the brim of the receptacle and of the arms has been removed in front, leaving a portion of the coalesced arms partially surrounding the proboscideal plated integument that covers the upper part of the receptacle; the figure is from Mr. Miller's work, and is introduced to illustrate the structure of these crinoideans.[285]

[285]Miller's Crinoidea,fig.N. pp. 98-100.

The external surface of the plates of the receptacle in the Actinocrinites, is generally covered with radiated markings and ridges, so that detached plates have been mistaken for those of Marsupites; see the restored figure of a Nave Encrinite,Wond.p. 654. In some species the receptacle is richly ornamented; but in the specimen figured,Lign.94,fig.1, the surface has been defaced in consequence of the fossil having been immersed in strong acid.

Cyathocrinus(Cup-like Encrinite).Lign.95, andLign.92,fig.2.—The column is formed of round, depressed, perforatedjoints, articulating by radiated surfaces; pentagonal near the summit. The receptacle is composed of five pieces, succeeded by two successive series of five plates, with intervening plates, and supports five bifurcating, radiated arms.

Lign. 95. Cyathocrinites planus;nat.Mountain Limestone, Clevedon.

The Encrinites of this genus have a light and elegant appearance: the forms of the plates composing the pelvis, and of the ossicula of the arms, are shown inLign.92,fig.2; which represents a specimen ofC. planus, from the magnesian limestone of Somersetshire; a beautiful example of the same species is figured inLign.95. The receptacle resembles in shape a depressed vase; its upper part was probably covered by a plated integument, having an aperture in the centre as in the Actinocrinites. Cyathocrinites occur in the Silurian, Devonian, and Carboniferous formations.[286]

[286]A figure of Cyathocrinus rugosus is given in Pict. Atlas, pl. xlix.fig.4. The same work contains coloured figures of Pentacrinus scalaris (Goldfuss), pl. xlvii. figs. 57, 64, 66; Pentacrinus basaltiformis, pl. xlvii.fig.47.A remarkable receptacle, with the tentacula partially introverted, is figured Pict. Atlas, pl. xlvi.fig.2, from Gloucestershire; and several beautiful examples of the arms, tentacula, &c. of Pentacrinites in Lias limestone and shale, in pl. li. figs. 9, 15, 16, and pl. lii. figs. 1, 2, 3, from Charmouth.

A remarkable receptacle, with the tentacula partially introverted, is figured Pict. Atlas, pl. xlvi.fig.2, from Gloucestershire; and several beautiful examples of the arms, tentacula, &c. of Pentacrinites in Lias limestone and shale, in pl. li. figs. 9, 15, 16, and pl. lii. figs. 1, 2, 3, from Charmouth.

Rhodocrinus.(R. verus.Pict. Atlas, pl. xlix.fig.7, 8.)—A beautiful form, allied to the Antinocrinoids, occurs in the palæozoic rocks, and is named the Rose-encrinite by Miller. The column is cylindrical and traversed by a pentagonal canal. The rays or arms arise by a single ossicle and then bifurcate: the receptacle is formed of three, five, ten, and more numerous series of plates, which are ornamented externally. A fine example of a crinoid of this type (Hypanthocrinus) from the Wenlock limestone, is figured in the London Palæontological Journal, pl. xxi.

In Sir R. Murchison's Sil. Syst. all the crinoids of the Silurian deposits, then known, are figured. Several new genera are described by Professor McCoy, in the Synopsis of British Palæozoic Fossils.

Eugeniacrinus(Clove-like Encrinite).Lign.92,fig.1.—These little crinoids, which resemble a clove in form, are found at Mount Randen, in Switzerland, in Oolitic limestone. The receptacle is simple in structure, for it has but one series of plates; its cavity is very small. It had five arms: the articulating surface of the ossicles is radiated. When perfect this crinoidean must have somewhat resembled the Lily Encrinite, but the plates are all anchylosed, or blended together, which Mr. Miller attributed to an early stage of growth.

PENTREMITES PYRIFORMIS.

Pentremites pyriformis(Pear-shaped angular Encrinite).Lign.91,fig.2.—The column of this remarkable crinoid is short, and formed of cylindrical, perforated ossicula, with radiated surfaces, and has irregular side-arms. The receptacle is composed of polygonal plates, divided by five perforated grooves or furrows, which are of an elongated petalous form, and converge in a rosette on the summit. The marginal longitudinal rows of minute pores are not however for the passage of soft membranous feelers, as in the ambulacra of echinoderms, as was formerly conjectured, but are channelsfor the transit of vessels that supply an infinite number of delicate simple tentacula, composed of extremely minute calcareous ossicula, as in the other Crinoidea, but not subdivided as in the Pentacrinites and Encrinites.

These articulated tentacula are arranged close together in longitudinal rows on the ambulacral spaces; there being two rows, each consisting of fifty tentacula, on every space. They are directed upwards towards the vertex of the receptacle, and appear to be the instruments for the capture and conveyance of food to the mouth.[287]

[287]See Dr. Fred. Röemer on jointed tentacles found on the ambulacral spaces ofPentremites, "Geol. Journal," vol. v. p. 8.

There are several species of Pentremites, some of which swarm in the cherty limestones of Kentucky. Mr. Say, to whom we are indebted for the first satisfactory investigation of these fossils, mentions that such is their abundance, that he has observed, on a piece of rock not larger than three inches by two-and-a-half, above twenty specimens lying in relief

Cystidea.—In the ancient fossiliferous strata there occurs a remarkable family of crinoideans, which is supposed to be restricted to the palæozoic ages; these fossils have been named by Von Buch,Cystideæ, from the body of the animal being wholly inclosed in a cyst, or box. The receptacle is of a spherical form, and composed of polygonal plates, articulated to each other; it has distinct apertures for the mouth, vent, and oviduct; the orifice of the latter is closed by valves. It has a short pedicle, but no arms have been discovered, and the Cystideæ are generally described as Crinoids without appendages of this kind. But in some members of this group, there are not only arms and tentacula, but likewise certain organs connected with the plates, which Prof E. Forbes terms, "pectinated rhombs," the functions of which are not obvious. The arms more closely resemble those ofthe Ophiuridæ than of the Crinoidea.[288]This order comprises several genera, and is the type under which the Crinoidea first appear in the natural records of our planet, according to the present state of our knowledge, and which becomes extinct before the advent of the Pentacrinites.

[288]See a memoir on the British Cystidea, by Prof. Ed. Forbes; in the Mem. Geological Survey, vol. ii.

MARSUPITES MILLERI.

Marsupites Milleri.Lign.92,fig.3,Lign.96.(Wond.p. 652.)—The fossil remains of a genus related to the Encrinites, but separated from them by being unattached and free, having no column of support, were first described by the late Mr. Parkinson under the name of "Tortoise Encrinite" (Org. Rem.vol. ii. pl. xiii.fig.24,Pict. Atlas, pl. xlvii.); but misled by the resemblance of some of the plates to those of certain species of Actinocrinites, Mr. Parkinson supposed the original to have possessed a jointed column. The examination of specimens obtained from the Chalk of Lewes and Brighton, enabled me to determine the true characters of the original; the purse-like form when the arms are closed suggested the name Marsupites (purse-like), by which it is now generally known; the specific nameMilleri, is in commemoration of the late excellent and able author of the Natural History of the Crinoidea.

The receptacle of the Marsupite is of a sub-ovate shape, and rounded and entire at the dorsal extremity; a large central plate forms its base, on which is placed a successive series of pentagonal and hexagonal plates, the margins of which are in contact, but not anchylosed nor firmly united; to the periphery of this cup are articulated five arms, which subdivide into ten rays, or tentacula. The top of the receptacle was closed by an integument, covered by numerous small semilunar plates, in the centre of which was situated the oral aperture. The external surfaces of the plates of the receptacle are generally granulated and radiated, as inLign.92,fig.3; but in some specimens the surface is quite smooth, a character which possibly may be specific. Some exampleshave the surface granulated and rugous, and these Mr. Miller regarded as distinct, and namedM. ornatus. I have not of late years been able to obtain specimens to determine this question.

The Marsupites vary in size, from an inch to three inches in length, exclusive of the arms. The receptacle is relatively very capacious compared with that of other crinoideans. The central plate is large, and of a pentagonal form, without the slightest indication of any column or process of attachment: five pentagonal plates are united to the sides of the basal plate, and above these a like number of hexagonals, which receive the five upper plates that constitute the margin; these have each a semilunar depression, to articulate with the first bones of the arms, or brachial appendages.

Lign. 96.—Marsupites Milleri,nat.Chalk, Lewes.

Detached plates and ossicula of marsupites are not uncommon in the Chalk of Kent and Sussex; nearly entire receptacles, filled with chalk or flint, are occasionally found in the pits near Lewes and Brighton; but examples with remains of the arms are extremely rare; and I have seen but one specimen (which I collected from the Sussex chalk), in which the plates of the integument that covered the opening of the receptacle are preserved.[289]

[289]It is figured in mySouth D. Foss.pl. xvi.fig.6.

The Marsupite is an exceedingly interesting type, in a zoological point of view, since it forms a link that unites the Crinoidea with the Comatulæ, or feather-stars, which we shall presently notice. Its general form and habits are sufficiently indicated by the numerous specimens that have been collected in the Chalk of the south-east of England.

The body of the animal was inclosed in a crustaceous case formed of large plates, articulated to each other by suture; the mouth or oral aperture was situated in the centre of the plated integumental cover of the receptacle. The organs of locomotion and prehension consisted of five arms or brachial appendages, formed of ossicula as in the crinoidea, and the whole was invested with soft tissue or integuments. When floating in the water, the creature could spread out its tentacula, and form a net to capture its prey, and by closing them, secure it, and convey it to its mouth. The figure,Lign.96, is restored from specimens which separately exhibit the parts here represented in connexion.

Fossil Asteriadæ.

FOSSIL ASTERIADÆ.

The radiated animals, popularly calledStar-fishes, from their stellular forms, are so abundant on our coasts, that the common five-rayed species must be familiar to all my readers who indulge in rambles on the sea-shore, and will serve as an illustration of the general appearance and structure of the beings whose petrified remains now claim our attention. This species belongs to the division of Asteriadæ, in which the rays are elongated, and far exceed in length the diameter of the disk; in another group (Goniastea, or Cushion-star), the body is angular, and the lobes or rays are short, and not longer than the diameter; while in a third subdivision (ComatulaandOphiura), the arms are distinct from the body, and articulated, elongated, and ramified, as in theCrinoidea.

The external surface of the common Star-fish is soft, and attached to a tough coriaceous integument, investing a skeleton composed of an infinite number of calcareous ossicula, arranged in regular series along the margins of the rays. Each ray has a longitudinal furrow, perforated at the sides by alternating rows of pores, through which tubular tentaculaare protruded. The mouth is situated in the centre of the under surface. Now if we imagine a Star-fish placed with its mouth upwards, and the five rays fringed with long articulated tentacula, as in the Comatula, and fixed by the centre of its dorsal surface upon a jointed stem, we shall have the essential characters of a crinoidean; and the animals of one recent tribe ofAsteriadæare actually in this condition in the earlier stage of their existence: these are theComatulæ, or Feather-stars, in some of which (theEuryale), the arms are as numerously subdivided as in the Pentacrinites.[290]

[290]The reader interested in this subject should peruse the charming volume on British Star-fishes and other Echinoderms, by Professor Edward Forbes. 1 vol. 8vo. John Van Voorst. 1841.

From the importance of the Crinoidea in the economy of the ancient world, the history of the only type at present inhabiting Europe, the ancient seas of which swarmed with numerous forms of these beautiful creatures, presents many points of interest. The receptacle of the soft body of theComatula, like that of the Crinoideans, consists of a cup-shaped calcareous base, which sends off from its margin five arms, that quickly subdivide, and are beset on each side with rows of articulated pinnæ; on the convexity there are also numerous slender, jointed, simple, tentacula. The mouth is situated in the centre of the area surrounded by the arms, and is capable of being elongated into a proboscis. In the young state, the Comatulæ are attached by a jointed stem to other bodies, as shown inLign.91,fig.1, which represents several of the natural size;fig.1ais an enlarged view of an individual, and closely resembles an expanded Crinoidean. The stem is composed of about eighteen joints, which are pentangular; after a few weeks the Feather-star becomes detached from its peduncle, and ranges the sea in freedom.[291]

[291]The researches of J. V. Thompson, Esq. first brought to light these interesting facts in the Natural History of the Comatula; this eminent naturalist first observed pedunculated Comatulæ in the Cove of Cork. When this discovery was first made known to me, I suspected that theMarsupitemight have been pedunculated when young; but as very small specimens of this Crinoid are equally free from all traces of a stem as the adult, I was led to relinquish that opinion: still the collector, when searching for Crinoidean remains, should bear in mind the possibility of this having been the case.

In the Comatulidæ, the arms are distinct from the body; these animals therefore closely approach the Crinoideans: in the true Star-fish, the angular processes, or arms, are an integral part of the body, containing a portion of the stomach, ova, &c., and are furnished with rows of pseudopodia.

Fossil Comatulæ have been discovered in the Solenhofen slate; and it is not improbable that some of the numerous Crinoideans may be Asteriadæ in the early stages of development.

In another group, Asteriadæ, (namedOphiuræor Serpent-stars,) the rays are long and slender, and without grooves or tentacula, and are distinct from the body. These organs are extremely flexuous, and in some species beset with spines, and enable the animal to seize and entwine round its prey. The mouth is central, and there is an ovarian aperture at the base of each of the five arms.

Though the fossil Star-fishes comprise many extinct genera, they belong to the same families as the recent; and Comatulæ, Ophiuræ, and Asteriadæ, occur in the Lias, Oolite, and Chalk, in considerable numbers. Professor Edward Forbes has determined many of the British species, and it is to be hoped, will publish a monograph on the Fossil Asteriadæ, as a companion to his delightful work on the recent Star-fishes.

FOSSIL OSSICULA OF STAR-FISHES.

Fossil Ossicula of Star-fishes.—From the immense number of little bones which enter into the composition of the skeleton of a single Star-fish, and which are but slightly held together after the death of the animal and the decompositionof the soft parts, we can understand how layer upon layer of ossicula of Asteriadæ may have been formed at the bottom of the cretaceous seas; as we find them in the quarries near Arundel, Worthing, &c. Whoever has witnessed the hauling up of the dredge off our coasts, and seen the mass of living Star-fishes which it brings up, as if the sea-bottom were a living bank of these Radiata, will not be surprised at the vast quantities of their fossil remains. This profusion of the living animals of this family, serves also to account for the enormous amount of those kindred but extinct forms, whose relics were the subject of investigation in the former part of the present chapter.

The ossicula vary in shape in different parts of the skeleton, and Prof. E. Forbes affirms, that the careful determination of their characters is of great importance, since they are the only paints of the animals likely to be preserved, and the shape of an ossicle is as truly indicative of a genus or species, as is that of a bone among the vertebrata. There is one ossicle situated on the side of the centre of the disk, which is worthy of remark, because it often occurs in the chalk mingled with the debris of the rest of the skeleton, and should be preserved by the collector. It differs from all the other bones in being marked with radiating grooves, and is called the madreporiform tubercle; it appears to be the analogue of the stem of the Crinoideæ, in other words, a rudimental condition of an organ, which is fully developed in that order of radiata.

OPHIURA.

Ophiura.Lign. 97, fig. 1.—Several species of this genus, which is distinguished by the long, slender, serpent-like arms, and the circular disk covered with plates and spines, have been found in a fossil state: one species was discovered in the Lower Silurian deposits by Prof. Sedgwick, and other forms have been obtained from all the succeeding formations. The Lias near Lyme Regis and Charmouth has yielded manybeautiful examples ofOphiura Egertoni. Professor John Phillips has figured a species (Oph. Milleri, Geol. York, pl. xiii.) from the marlstone of Yorkshire, and a species from the Oxford Clay has been described asOphiura Prattii. In the Cretaceous formation, remains of several species have been found. The first specimen from the Sussex Chalk that came under my notice, was discovered many years since, by my son, in a quarry at Preston, near Brighton; the rays were admirably preserved, as shown in the portion figured inLign.97. An example of this species, with the disk entire, and portions of five arms, was found by Henry Catt, Esq. and is represented in pl. xxiii.fig.2, of Mr. Dixon's work.[292]

[292]Three plates are devoted to the Cretaceous Star-fishes: the descriptions by Prof. E. Forbes comprise twenty-five species, belonging to the genera Oreaster, Goniaster, Stellaster, Arthraster, and Ophiura, all from the Chalk of Sussex and Kent.

Lign. 97. Fossil remains of Star-fishes.Fig.1a.—Part of the ray ofOphiura serrata;nat.Chalk, Preston.(Mr. Walter Mantell.)1.—Portion of the same magnified.2.—Goniaster Hunteri.Chalk. Gravesend.

GONIASTER—ASTERIAS.

Goniaster.Lign.97and98.—The star-fishes of this genus, popularly called Cushion-stars, are of a pentagonal form, and have a double series of large marginal plates, bearing granules or spines; the latter are seldom preserved in the fossils. The upper surface is nodulose.

Lign. 98. Fossil Star-fish.Chalk, Kent.Goniaster Mantelli.(sp Forbes.[293])

[293]Dixon's Cret. Foss. p. 332.

The detached ossicula of the skeletons of Cushion-stars are frequent in the White Chalk; and the large central bone, themadreporiform tubercle, which is present in the dorsal aspect of all star-fishes, is large, and therefore often observed, and may be easily mistaken for the base of a crinoidean receptacle. The layers in the Sussex Chalk composed of the exuviæ of star-fishes, as previously mentioned, are chiefly made up of ossicula of goniasters.

There are two species not uncommon in the Chalk, of which portions may generally be obtained from the pits near Gravesend; and occasionally very fine examples of the entire goniaster are met with. Mr. Dixon's work contains figures of several exquisite fossils of this kind. These organic remains were familiar to the early collectors: Mr. Parkinson figures several in Org. Rem. vol. iii. pl. i. and ii.[294]

[294]Pict. Atlas, pl. liii.

Goniaster Hunteri(Lign.97), has the body obtusely pentagonal, and the sides nearly straight; the superior intermediate marginal plates are four, equal, broadly oblong,coarsely mamillato-punctate; the ossicula of the disk hexagonal.[295]This species is common in the upper chalk.

[295]Prof. Forbes, Dixon's Cret. Foss. p. 331.

InGoniaster Mantelli,Lign.98, the body is pentagonal, but the sides are curved, with projecting angles; the ossicula of the disk are punctated. The superior intermediate marginal plates are oblong, narrow, punctate, marginate, and six in number.[296]

[296]Ibid. p. 332.

Specimens of these Goniasters are sometimes met with attached to a nodule of flint, in an extraordinary state of freshness; sharp imprints of the external surface, the skeleton having perished, are also found in flints, and, rarely, casts in pyrites. The whetstone of Dorsetshire often bears distinct moulds of Goniasters! I have found ossicula of this form of Star-fish in the London Clay of the Isle of Sheppey.

Asterias.Lign.99.—The animals of this genus, of which the common Star-fish is the type, are stellate in form; the rays are flat, and extend from the body, of which they are a prolongation—not mere appendages. They have deep grooves or furrows bordered by marginal plates, which are continued to the extremities.

The Lias of Germany has yielded several species of Asterias; one of which is figured,Lign.99. A very large species occurs in the Cornbrash of the Oolite of England. A magnificent specimen ofAsterias arenicola(Goldfuss), from the calcareous grit, near Pickering, Yorkshire, measuring 101/2inches from the extremity of one ray to that of another, is figured in the London Palæontological Journal, pl. xvii. The same work contains admirable figures ofOphiura Egertoni, andOph. senatuin flint, pl. xix.;Oph. Milleriin Staithes marlstone, andOph. Murravii, pl. xx.; and two specimens ofOph. Millerion the same slab of Lias from Staithes, near Whitby, pl. viii.

The Star-fishes of the British palæozoic strata are described by Prof. E. Forbes in the Memoirs of the Geol. Survey,Decad.1.[297]

[297]See also Prof. M'Coy's Lower Palæozoic Fossils, p. 58.

Lign. 99. Fossil Star-fish.Lias, Wirtemberg.Asterias prisca.(Goldfuss.)

GEOLOGICAL DISTRIBUTION OF CRINOIDEA.

Geological distribution of the Crinoidea.—The great number of extinct forms of this order of Radiata in the most ancient fossiliferous deposits, is a remarkable fact, which has already been incidentally adverted to. In the palæozoic seas—including the Silurian, Devonian, Carboniferous, and Permian—the Crinoidea were represented by upwards of fifty genera, whose existence began and ended during that geological cycle.

According to the present state of our knowledge all those peculiar types of radiated animals were created, and each lived through the destined period alloted to its race, and died out ere the deposition of the New Red Sandstone; not a single species, not a relic of the innumerable individuals that swarmed in the palæozoic oceans, has been observed in any strata above the Permian.

The Trias, which ranks as the earliest of the secondary formations, is characterized by the advent of two typical genera; the true Encrinus or Lily-encrinite, and the Pentacrinus; the former is unknown in any other deposits; the duration of its race was comprised within the Triassic epoch. The Pentacrinus, on the other hand, has been perpetuated through all the succeeding periods, and one species inhabits the present seas; the sole existing representative of the most ancient type of this order.

In the Oolite, another living form, the Comatula, first appears.

The ocean of the Cretaceous epoch was inhabited by five genera of Crinoids, unknown elsewhere; among them is that remarkable genus, the Marsupite.

The Crinoidea of the Tertiary seas are as few in number and variety as those of the present day; not a vestige of any of the ancient tribes has been discovered. M. D'Orbigny'sTab.12 presents the phenomena thus briefly noticed, in a striking point of view.

From this review of the fossil Crinoidea and Asteriadæ, the student will be in some measure prepared for the collecting of instructive specimens from the immense accumulation of remains imbedded in certain strata of the Oolitic, Liassic, Carboniferous and Silurian rocks.

The British species of fossil Crinoidea amount to more than two hundred, and when the great number of bonesthat enter into the composition of the skeleton of a single Pentacrinite or Encrinite is considered, the prodigious quantity of the fossil remains of these zoophytes in the ancient deposits may be readily conceived. Polished slices of the encrinital marbles of Derbyshire, and of the Lias limestones from Lyme Regis and Charmouth, should be obtained, as they show sections of the imbedded crinoidal stems and detached ossicula; and sometimes of the receptacles.

FOSSIL ECHINIDÆ, OR SEA-URCHINS.

Lign. 100. Turban Echinus, with its spines;1/2nat.(Hemicidaris crenularis, Agassiz.)Jura limestone.

The fossils we have now to examine are among the most familiar of the objects commonly known as petrifactions; for as the enveloping cases of the Echini possess considerable durability, they have served as moulds into which silex, calc-spar, limestone, pyrites, and other mineral substances, when in solution, or in a semi-fluid state, have percolated, and formed sharp and enduring casts, which exhibit the forms of the plates, and the disposition of the pores, striæ, &c. of the original structures.

The common Echinus of our sea-coasts (Echinus sphæra), known by the name of Sea-egg, Sea-urchin, or Sea-hedgehog, presents the typical characters of this order of Radiata, which differs from the Crinoids and Star-fishes in the absence of arms.

The calcareous envelope of the Echinus, or shell, as it is popularly called, is composed of many calcareous, polygonal plates, closely fitted to each other, and arranged in regular and elegant patterns; appearing in the globular and spherical kinds like the lines of the meridian on a globe. The plates are disposed in ten vertical series, united by serrated sutures, and form sections, into which the envelope or case very commonly separates upon the decay of the investing integuments. Of the ten bands five are large and five small. The large bands (areæ) are each composed of a double row of plates, ornamented with tubercles supporting large spines (Lign.100). The five narrower bands consist of much smaller plates, and the spines are minute, or altogether wanting; hence these bands appear like avenues through the spinous tracks, and have therefore been fancifully termed ambulacra or walks. They are the equivalents of the grooves or furrows of the Star-fishes (Lign.108,a.); and are traversed by numerous pores, for the exsertion of tubular feet, or tentacula. Besides these rows of minute openings, there are two principal apertures, the mouth and the outlet or vent; and also a few large pores, commonly five, on the summit, for the exclusion of the ova, and the free admission of water.

The form and relative position of the parts above described, afford characters by which the order is divided into genera. The mouth, which is situated on the lower part, is in some species furnished with five sharp angular teeth, attached to a calcareous framework that admits of being protruded; this apparatus, when entire, commonly bears the name of "Diogenes' lantern." The eminences on the surfaceof the plates vary in size from mere granules, or papillæ, to large mamillated tubercles; they serve for the attachment of movable spines, which also present great variety of form and ornament. The spines have a cup-like cavity at the base which fits on the papillæ, and in many species are only supported by the capsular envelopment of the common integument; but in others, the large spines are attached by a ligament which passes from the centre of the socket, and is received in a perforation of the papilla of each tubercle, in the same manner as theligamentum teresof the human thigh-bone. Transverse slices of the spines exhibit the internal structure, and are beautiful objects under the microscope.

There are also minute appendages to the integument, calledpedicellariæ, or pinchers, of a very remarkable character, whose functions are not known. They are slender columnar bodies, each crowned with three calcareous teeth-like spines, beautifully sculptured, and which in some species are long and slender, in others short and obtuse. I have not observed any traces of these bodies, even in the best preserved echinites, but as they are as durable as the spines and case, they may exist in a fossil state.

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