CHAPTER XIV.

[495]PalÃ¦ontologists are particularly indebted to the Rev. P. B. Brodie, F.G.S. for his compendious and valuable "History of the Fossil Insects in the Secondary Rocks of England" (8vo. 1845); and to J. O. Westwood, Esq. the eminent Entomologist, for the very important and interesting Observations on the Insect Remains, prefixed to the above work. In an interesting paper on the Geology of the vicinity of Ilminster, C. Moore, Esq. has noticed the numerous Insect remains of the Upper Lias of that place. Prof. E. Forbes and W. R. Binfield, Esq. have discovered Insects in the Hastings series; and Mr. Binfield, besides having most successfully searched the Upper Lias of Gloucestershire, has also detected some specimens in the Lias at Lyme. Lastly, Mr. Morris has found Insects in the Upper Lias in Lincolnshire.

ARACHNIDA.

Fossil Scorpion.(Bd.pl. xlviâ€².)â€”The discover of a fossil Scorpion in coal-shale, associated with leaves, by Count Sternberg, and of Spiders in the limestone of Solenhofen, by Count MÃ¼nster, proves the existence at a very remote period of both these insectivorous families ofArachnidans, or spiders (Bd.p. 405). The fossil Scorpion was found in a block of argillaceous shale, at Chomle, in Bohemia. It lies imbedded amidst the carbonized remains of leaves, and a large trifid carpolithe or seed-vessel (seeBd.pl. xlviâ€².): by a fortunate separation of the shale, the back or dorsal carapace is shown on one surface; and the thorax, with five or six legs attached, and the abdominal segments, are exposed on the other, together with a fragment of the tail of another and larger Scorpion. The head and eyes, one of the jaws with teeth, and a portion of the skin remain (Bd.pl. xlvi. figs. 3, 4, 5, 6). The horny covering seems to have undergone no change; it is still elastic and transient, and consists of two layers, both retaining their texture, and structure, and exhibiting under the microscope hexagonal cells divided by strong partitions.

Fossil Spiders.â€”With the numerous insects preserved in the gypseous marls at Aix, of which we shall treat hereafter, Spiders are occasionally found. A beautiful example, showing the under surface of a small spider, with the papillÃ¦ of the spinning organs protruded by pressure, from the cabinet of Mrs. Murchison, is figured,Bd.pl. xlviâ€². fig 12 In the beautiful lithographic stone of Solenhofen the remains of spiders are not unfrequent.

INSECTA.

Fossil Neuroptera.â€”Of this order, the insects of which are distinguished by their four finely reticulated membranous wings, several fossil species have been found. Some of these are referable to the family LibellulidÃ¦;â€”insects so well known from their light and elegant figure, their beautiful and variegated colours, their large lustrous wings, and the velocity and gracefulness of their motions.

Lign. 179. Fossil Libellula, or Dragon-fly.Solenhofen.(Drawn by Mr. Joseph Dinkel.)In the cabinet of the late Marquess of Northampton.

Fossil LibellulidÃ¦.Lign.179.â€”Of the highly organized family of carnivorous insects, theLibellulidÃ¦, five or six specimens have been discovered in the lithographic limestone of Solenhofen; a beautiful specimen from thatlocality is represented,Lign.179. In this example both pairs of wings remain, but one wing is pressed down beneath the abdomen: the nervures of the wings are admirably preserved.

A few examples of the remains of this family have been found in the British strata. One species ofLibellulaand one ofÃ†shnahave been found by the Rev. Mr. Brodie in the Purbeck beds of the Vale of Wardour. Two species ofLibellula,[496]two ofÃ†shna, and some other allied species have been obtained by Messrs. Strickland, Buckman, Binfield, and Brodie from the Lias. The wing of theÃ†shna liassina, discovered in the Lias, near Binton, in Warwickshire, by Mr. Strickland, is two inches and ten and a half lines in length, and eight and a half lines in its greatest breadth, being one-third larger than the wing of the largest British species. SeeWond.Lign.119, and p. 528.

[496]A very interesting specimen of fossilLibellula, discovered by the Rev. Mr Brodie in the Upper Lias near Cheltenham, is figured in the Quarterly Geol. Journal, for 1848, vol. v. pl. v.

Fossil Corydalis.Lign.181,fig.2.â€”The wing of a remarkable fossil Neuropterous insect was discovered by me in a nodule of ironstone, from Coalbrook Dale, and mistaken for a leaf. The specimen consists of one wing, which, as M. Audoin first ascertained, closely resembles that of the livingCorydalisof Carolina; seeLign.181,fig.2. The membranous structure and the distribution of the nervures are distinctly preserved; on the portion figured the surface of the wing lies in relief on the stone; and on the corresponding part of the nodule, a sharp imprint remains,[497]I have named this fossil in honour of the eminent French savant, M. Alex. Brongniart.

[497]This specimen is now in the collection of the British Museum.

Wings ofCorydalishave also been found in the Purbeck beds of the Vale of Wardour, by the Rev. Mr. Brodie, whohas also discovered remains ofPhryganeidÃ¦and aTermesin the same group of strata.

Panorpa ? Liassica.Lign.180.â€”In the Lias, on the banks of the Severn, at Wainlode Cliff, Gloucestershire, specimens of minute neuropterous wings have been discovered. I subjoin accurate figures of two specimens in the cabinet of the Geological Society; they are represented twice the natural size; they resemble the wings of a recent genus of Neuroptera, termedPanorpa; particularlyP. Germanica. The transverse lines are not fractures, but nervures, and are faithfully copied from the originals.

To the above notice of British fossil neuropterous insects, I may add that the wing of a large species (Hemerobioides giganteus) has been discovered by Dr. Buckland in the Stonesfield slate.

Lign. 180. Wings of Neuropterous Insects.Twice nat. size.(Drawn by S. P. Woodward, Esq.)Lias.Wainlode Cliff.Portions of the anterior wings of a species resemblingPanorpa.

Lign. 181. Fossil Wings of Insects.(Drawn by S. P. Woodward, Esq.)Fig.1.â€”Elytron, or wing-case ofBuprestis Bucklandi,Great Oolite;Stonesfield.2.â€”Wing ofCorydalis Brongniarti. (G. A. M.)Carboniferous;Coalbrook Dale.

Fossil Coleoptera.â€”Theelytraor wing-cases of coleopterous insects have long since been noticed in the oolitic slate at Stonesfield, near Oxford; a locality celebrated for the only mammalian relies hitherto discovered in the Secondly strata of England. The Stonesfield elytra are always found detached; in no instance, I believe, has any other part of an insect been observed, except a single leg of aCurculio(Bd.pl. xlviâ€².fig.10). The specimen figuredLign.181,fig.1, displays the usual characters of the largest species. These fossils are of a reddish-brown colour, with a finely granulated surface; there appear to be four or five species, all of which belong toBuprestis, a family of beetles remarkable for their splendid metallic lustre. Remains ofColeopteraoccur in the Tertiary clays near Corfe, Dorset,[498]and in the Lias of Worcestershire and Gloucestershire; and in the Danby oolitic coal-pits, in the eastern moorlands of Yorkshire, the elytra of beetles have also been discovered, by Mr. R. C. Taylor (Bd.vol. ii. p. 78).

[498]See Notice by the Rev. Mr. Brodie, Quart. Geol. Journ. vol. ix. p. 51.

A most remarkable fossil of this kind is described by Dr. Buckland; a unique specimen ofBuprestis, from Japan, about an inch long,converted into chalcedony, with the antennÃ¦ and portions of the legs finely preserved. The surface of this insect is covered with clusters of minute concentric rings of chalcedony; an appearance common in silicified shells. Associated with this fossil, were fragments of silicified wood, bored with tubular cavities, apparently by the larvÃ¦ of insects of this family; and within these cavities was a quantity of dust produced by the boring, also converted into chalcedony (Bd.vol. ii. p. 78).

Of theCurculio, a genus of coleoptera distinguished by their splendid elytra, of which theDiamond Beetleis a familiar example, the remains of two species have been discovered in the nodular ironstone of Coalbrook Dale, by Mr. W. Anstice, and are figured and described by Dr. Buckland (Bd.vol. ii. p. 76; and pl. xlviâ€². figs. 1, 2). In one of these specimens (Curculioides Ansticii), with the exception of the rostrum and anterior part of the head, all the essential characters of the insect are displayed; namely, the elytra, thorax, and six legs, the hindmost of which exhibits the enlarged femur, or thigh, a character peculiar to theCurculionidÃ¦. The legs possess a tufted appearance, which that eminent entomologist, Mr. Curtis, conceives may have been caused by fungi, after the death of the animal, as often happens in tropical climates. In the other example (C. Prestvichii), the insect lies on its back, with the left side raisedupwards, and exhibiting a portion of the external surface of the left elytron; there are remains of the antennÃ¦, and indications of the proboscis and of the legs.

Lign. 182. Insectiferous Limestone.Purbeck.(Magnified six diameters.)a, b.Membranous wings of theCorydalistype.c.Punctate-striate elytron of a Beetle.d.Elytron of a Beetle, with a smooth surface.e.Smooth elytron, the upper part impressed with transverse lines.

TheOrthoptera,Homoptera, andDipteraare also represented in the Lias of Gloucestershire, and in the Purbeck strata of the Vale of Wardour, by numerous species, which have been enumerated, and mostly discovered, by the Rev. Mr. Brodie.[499]This observer has, indeed, been very successful in his researches in the latter locality, for in the deposits of limestone and marl which yielded the isopodous crustaceans, previously described (p. 521,Lign.171), he hasdiscovered the remains of several orders of insects, and states that, for abundance and variety of specimens, the beds may be said to resemble the Tertiary marls of Aix and Å’ningen. These remains were obtained from a quarry at Dinton, about twelve miles west of Salisbury. They consist chiefly ofColeoptera, with the remains ofNeuroptera,Trichoptera, andHomoptera, and of several species ofDiptera. In the cream-coloured laminated Purbeck marls that axe exposed in Durlstone Bay (about one mile from Swanage) insectiferous beds have been found by the Rev. O. Fisher and Prof. E. Forbes, which are the equivalents of those of the Vale of Wardour; and similar beds were met with in the cutting of the railway through the Ridgway Hill, between Dorchester and Weymouth.

[499]See Brodieâ€™s Fossil Insects.

In a quarry on the road-side between the village of Stone and Hartwell, Bucks, the Portland Oolite is covered by the Purbeck marls; in these latter remains of Insects occur, together with scales and teeth of small Fishes, and abundance ofCyprides.

All the British localities of fossil insects have now been alluded to; but on the Continent, independently of the celebrated limestones of Solenhofen, to which reference has been made,p. 550, there are several tertiary deposits exceedingly rich in these interesting fossils.

FOSSIL INSECTS.

Fossil Insects of Aix, in Provence.â€”The town of Aix is situated in the lowest part of a deep valley, the immediate flanks of which are composed of a thick fresh-water formation, lying unconformably upon strata of Jura limestone. The fresh-water series consists of white and grey calcareous marls, calcareo-siliceous grits, and beds of gypsum; and the quarries formed in the latter rock have long been celebrated for the prodigious quantity of fish and plants which they contain. M. Marcel de Serres first made known the great abundance of insects in these gypseousmarls, and has enumerated nearly seventy genera, chiefly of the Coleoptera, Diptera, and Hemiptera; they are mostly referable to European forms, and to existing genera. An interesting Memoir on these strata, by Sir R. Murchison and Sir C. Lyell,[500]first directed the attention of the English reader to these beautiful fossils. InWond.p. 261, an epitome of this valuable communication is given, and five specimens of insects are here figured, which will convey some idea of their forms and perfect state of preservation.

[500]Edinburgh New Philosophical Journal for October, 1829.

Lign. 183. Fossil Insects.Tertiary.Aix in Provence.Fig.1.â€”Tettigonia spumaria.2.â€”Mycetophila; the body distended by pressure.3.â€”Lathrobium.4.â€”Allied toPenthetria holosericea. The hinder legs are broken off, and one of them reversed, so that thetarsinearly touch the thigh; thepalpiare long and perfect; the antennÃ¦ are remarkably distinct.5.â€”Liparus; resemblingL. Punctatus.

Fossil Insects of Å’ningen.â€”In the immediate vicinity of Å’ningen, near Constance, on the banks of the Rhine, there is the basin of an ancient lake, filled up with marls and limestones, presenting a fine example of a lacustrine formation, and abounding in fossil Fishes, Reptiles, Plants, Shells, Crustaceans, and Insects.[501]These Insects are often in an admirable state of preservation, and occur in the different stages of larva, pupa, and imago. The pupa of aLibellulashows the mask, insertion of the legs, and the spiracula. Some belong to genera, the species of which frequent marshy plants of the same kind as those which are found associated with the insects; and it seems probable that they fell into the lake from the plants which grew on its borders, and became enveloped in the fine mud or sediment. Numerous species of several genera of Ants also occur in these deposits of Å’ningen and at Radoboj in Croatia.[502]

[501]See the Memoir by Sir R. I. Murchison on the lacustrine formation at Å’ningen, near Constance, Geol. Trans, new series, vol. iii. p. 277.[502]See Prof. O. Heerâ€™s Memoir, translated in the Quart. Journ. Geol. Soc. vol. vi. pt. ii. p. 61; and his History of Insects, ibid. p. 68.

[501]See the Memoir by Sir R. I. Murchison on the lacustrine formation at Å’ningen, near Constance, Geol. Trans, new series, vol. iii. p. 277.

[502]See Prof. O. Heerâ€™s Memoir, translated in the Quart. Journ. Geol. Soc. vol. vi. pt. ii. p. 61; and his History of Insects, ibid. p. 68.

FOSSIL CADDIS-WORM.

Fossil LarvÃ¦ of Phryganea.Ly.p. 185.â€”TheCaddis-worm, so well known to all the brethren of the angle, is the larva of the winged insect termedPhryganea, and is abundant at the bottom of fresh-water streams and lakes; the cases, like those of the marineSabella(p. 385,fig.6), are always studded over with extraneous bodies, cemented together by a glutinous secretion to the silken integument, or case, which encloses the lava. Some species are coated with pieces of stick or straw, others with minute shells, as planorbis, bithinia, and the like; and when the larvÃ¦ have passed into the perfect state, their cases, orindusiÃ¦, remain.Many of the Tertiary fresh-water limestones of Auvergne are almost wholly composed of theindusiÃ¦of Caddis-worms, cemented together by calcareo-siliceous matter into stone, which is employed for building, and is called indusial limestone (Wond.p. 273). These limestones are associated with marls abounding in fresh-water shells and cyprides; the whole assemblage presenting all the stratigraphical and zoological characters of a lacustrine formation. "If," says Mr. Scrope,[503]"we consider that repeated strata, of five or six feet in thickness, almost entirely composed of these tubes, once extended over a district presenting a surface of many hundred square miles, we may have some idea of the countless myriads of minute beings which lived and died within the bosom of that ancient lake."

[503]On the Geology of Central France, by G. Poulett Scrope, Esq. 4 to. 1827.

On Collecting Fossil Insects.â€”The localities in which the British collector may reasonably expect to discover fossil remains of Insects, are Stonesfield, where the elytra of beetles are by no means scarce,â€”Coalbrook Dale, in which relics of this class are sometimes, but very rarely, found in the ironstone nodules,â€”Bedford, Warwickshire, and the Wainlode and Aust Cliffs, for Lower Lias insects,â€”Dumbleton and Ilminster, for Upper Lias insects,â€”Dallards, near Dinton, and Stone, near Aylesbury, and the exposures of similar beds in Dorsetshire, for the Purbeck insects.

The white clays belonging to the Bagshot series of Bournemouth, Poole, and Corfe, so rich in beautifully preserved leaves and other parts of plants, should be carefully searched for insect remains, since these clays at Creech, near Corfe, have already afforded a few specimens.[504]

[504]Quart. Geol. Journ. vol. ix. p. 51.

At page 549 a few other English localities yielding these delicate and very interesting fossils are also indicated as having been lately discovered by some of our most acute and active geologists.

Should the student visit the celebrated sites of these fossils in France and Germany, namely, Aix, Å’ningen, Solenhofen, &c., he will have but little difficulty in obtaining an interesting series, at a moderate expense.

The marls and limestones in which insects occur are often of a laminated character, and in general readily split asunder in the direction favourable for the display of the insects. In some examples, only the form of the animal is seen through a thin opaque pellicle of calcareous earth, which may be removed by a penknife or graver, and the wings, elytra, antennÃ¦, legs, &c. will thus be disclosed. A very thin coating of mastic varnish heightens the colours of such specimens, and renders them more durable.

FOSSIL ICHTHYOLOGY; COMPRISING THE SHARKS, RAYS AND OTHER PLACOID FISHES.

Lign. 184. A group of Fossil Fishes.Tertiary.Aix.Lebias cephalotes(Agassiz).

Ascendingfrom the two grand subdivisions of the animal kingdom, theMolluscaand theArticulata, we advance to theVertebrata, animals distinguished from all those which have previously engaged our attention, by the possession of a bony, jointed, hollow column of support, or spine, formed of bones termedvertebrÃ¦(turn or whirl bones), and enclosing and protecting those strands or cords of the nervoussystem called the spinal marrow; the former classes, being destitute of such a structure, have the general name ofInvertebrata.

In the beings whose mineralized remains form the subject of our present investigation, the durable parts of the frame-work, or skeleton, are, in most instances, situated internally, and their fossil relics consist principally of the bones, or solid earthy portions of their structures, either imbedded in the rocks in their natural relative position, or in a state of dismemberment and dispersion. In most cases the teeth, and in many the durable parts of their external integument, or skin, are also preserved, in a greater or less degree of integrity.

In the lowest class ofvertebrata, theFishes, the skin is covered with numerous pieces or scales, of a dense, durable substance, and strengthened, in some families, by the addition of osseous plates; thus constituting a flexible and almost impenetrable coat of armour, which affords suitable protection to beings peculiarly exposed to external injuries, from the nature of the regions they inhabit, and the state of warfare with each other in which they are constantly engaged. Confined to a fluid medium, they are provided with organs fitted for aquatic respiration, calledbranchiÃ¦, or gills, and with instruments of progressive motion, termedfins, by which they are enabled to propel themselves through the water with great velocity. The apparatus for seizing, tearing, and crushing their prey presents numerous and important modifications, corresponding to the habits and economy of the different genera; their teeth offering as great variety of form and structure as those of the higher orders of animals.

The cartilaginous or the osseous nature of the skeleton, and the number and position of the fins, were the characters formerly employed in the classification of Fishes; but Prof. Agassiz, conceiving the structure of the skin to afford anatural index to the essential modifications of organization and functions, has, with great sagacity, adopted an arrangement founded upon the form and structure of the scales; and he has divided the whole class into four orders, each distinguished by essential differences in the dermal (skin) system. To the geologist this method has proved of inestimable value; for it is simple, easy of application, and, so far as our present knowledge extends, may be relied upon as affording accurate conclusions as to the nature and relations of the originals to which a few detached fossil scales may have belonged. Another important aid has been derived from the microscopical examination of the structure of the teeth; and a splendid work on this subject by Professor Owen has opened a wide field of palÃ¦ontological investigation, which is yet but very partially explored.[505]

[505]Odontography; or, a Treatise on the Comparative Anatomy of the Teeth; their Physiological Relations, Mode of Development, and Microscopic Structure; illustrated by upwards of 150 plates. By Prof. R. Owen, F.R.S. &c. 4to. London. 1840-1845.

The living species of Fishes exceed eight thousand; and those found in a fossil state, and determined by M. Agassiz, already amount to upwards of one thousand five hundred; while several hundreds are still undescribed; and the rapid progress of geological research is continually adding to the number: upwards of six hundred British fossil species are enumerated. In an initiatory work like the present, it will be necessary to confine our remarks to an illustration of the mode in which the investigation of the fossil remains of the animals of this class should be conducted; and, by the elucidation of a few leading principles, prepare the student for the perusal of works expressly devoted to this branch of PalÃ¦ontology.[506]

[506]The admirable and important work entitled "Recherches sur les Poissons Fossiles, par Louis Agassiz," stands preeminent in this department of science. It consists of five volumes, 4to. of letter-press, and five volumes, folio, of coloured plates. It must be consulted by all who would acquire a correct view of the present state of fossil Ichthyology.It is from this work that the commentary in the text has been chiefly derived.

The fossil remains of fishes rank in the first class of the "Medals of Creation," for they demonstrate the existence of numerous tribes of highly organized beings in some of the most ancient fossiliferous strata, and the continuance of the same type of organization, variously modified, through the entire series of subsequent deposits to the present time. Each geological formation contains peculiar groups of fossil fishes, distinguished by distinct modifications of structure. Thus, according to the data at present obtained, all the osseous fishes anterior to the Chalk belong to genera which have no representatives among existing species; and they are characterised by rhomboidal scales covered with enamel.

The state of conservation in which the fossils of this class occur, appears to have depended on the relative delicacy or firmness of the original structures, and on the nature of the deposits in which the fishes were imbedded. Thus the fossil fishes of the early formations, which are characterised by their dense integument and enamelled scales, often present the entire forms of the originals, and generally considerable portions of the connected scales, with the fins and other appendages: while the specimens of later deposits, which contain a large proportion of species with delicate scales, more often display the mineralized osseous skeleton, than the dermal structure. Sedimentary strata composed of mud or fine detritus, of whatever age, have been most favourable to the preservation of the entire forms; hence we often find in the pulverulent clays and marls of the Tertiary strata, in the Chalk of England and Westphalia, and in the fine lithographic stone of Solenhofen, fishes perfect in form, and not only individuals, but groups, with the scales, fins, head, teeth, and even the capsule of the eye, in their natural positions. A small slab of marl from Aix, in Provence, inthe collection of Sir R. I. Murchison, contains scores of small fishes, as perfect as if recently imbedded in soft mud: a portion of this specimen is represented,Lign.184; and the beautiful fish figured in the frontispiece of vol. i. (pl. i.fig.3), from near Castellamare, will serve to illustrate the state of perfection of some of the ichthyolites of the Jura limestone. In the Chalk, many of the fishes are uncompressed, the body being as perfect in form as if the original had been surrounded by soft plaster of Paris while floating in the water. But in coarse limestones and conglomerates,â€”in other words, in materials that have been subjected to the action of the waves and torrents,â€”detached teeth, scales, bones, &c. constitute the principal vestiges of this class of beings.

In illustration of this department of Paleontology, it will be expedient to consider,â€”1stly, the characters afforded by the scales and dermal appendages; 2dly, the teeth, or dental organs; 3dly, the osseous and cartilaginous skeletons; and lastly, apply the data thus obtained to the elucidation of some of the principal fossil genera and species.

Scales of Fishes.â€”The dermal plates or scales are composed of two substances, disposed in laminÃ¦ or plates; the one cartilaginous or horny,â€”the other dense and osseous, possessing the structure of bone. In most species the scales are imbricated,i. e.lie over each other like the tiles of a roof; the margin of a front row partly covering the series immediately behind. From this arrangement, the apparent shape of the scales is very different from their true form; the processes of attachment and the lateral angles being concealed. The scales that are not imbricated are either very small, and imbedded in the substance of the skin so as to be imperceptible to the naked eye, as in the shagreen of Sharks; or are disposed in the form of bosses or scutcheons, as in the Rays; sometimes bristling equally over the surface of the body, as in theDiodon; and sometimes covering itlike mosaic work; or forming particular series on certain regions of the body, while the other parts are garnished with different scales, as in the Sturgeon. There are a few genera destitute of scales. In almost all fishes there is a particular series disposed in a gently undulated line along each side of the body, from the head to the tail, and constituting what is termed the lateral line; these scales are tubular, and serve an important purpose in the economy of these animals. Every one must be aware that the body in most living fishes is constantly covered with a kind of mucus, or slime, which serves to lubricate the skin and to defend it from the action of the surrounding medium. This fluid is secreted by a mucous canal or duct, which extends along the body, and ramifies in all the bones of the head, jaws, &c.; and it is distributed over the surface of the head by numerous pores in the bones, and over the body by the tubes formed by the row of scales above described.

Lign. 185. Fossil Scales of Fishes.(highly magn.)Chalk.Lewes.Fig.1.â€”Scale or plate of theshagreenof aShark.2.â€”Scale ofMacropoma Mantelli; the exposed surface.3.â€”Scale ofBeryx Lewesiensis; the exposed surface.4.â€”Scale ofOsmeroides Mantelli; the entire form.

The four orders into which this grand class of vertebrata is divided by M. Agassiz, are founded upon the peculiar structure of the scales;[507]and are characterised as follow:â€”

[507]For illustrations of the scales of fishes, seeWond.p. 339,Lign.68, and p. 340,Lign.69;Foss. Brit. Mus.p. 419; andLy.fig. 306, figs. 342-347, &c. And for their minute structure, see Prof. Williamsonâ€™s important paper in thePhil. Trans.for 1851.

Order I.Placoid(a broad plate).â€”The skin covered irregularly with enamelled plates, sometimes of a large size, but frequently in small points, as the shagreen on the dermal integument of theSharksand the tubercles of theRays.Lign.185,fig.1, a fossilplacoidianscale from the skin of a shark, highly magnified.

Order II.Ganoid(splendid, from the brilliant surface of the enamel).â€”The scales are of an angular form, and composed of plates of horn or bone, covered with a thick layer of enamel; their structure is identical with that of the teeth. TheSturgeonis an example of this order.Lign.196, figs. 1, 2, 3, 4, are fossil scales of aganoidianfish.

Order III.Ctenoid(toothed, or comb-like).â€”The scales are formed of plates, which are toothed or pectinated on their posterior margin or edge, like a comb. As the plates are superimposed on each other, so that the lowermost always extend beyond the uppermost, their numerous sharp points or teeth render the scales very harsh to the touch. ThePerchbelongs to this order.Lign.185,fig.3, represents a fossilctenoidianscale.

Order IV.Cycloid(circular).â€”The scales are composed of simple laminÃ¦, or plates of bone or horn, without enamel, and have smooth borders; but their external surface is often ornamented with markings. The scales of the lateral line consist of funnels placed one within the other; the contracted part of which, applied against the disk of the scale, forms the tube through which the mucus flows. To this order belong the Mullet, Salmon, and Carp.Lign.185,fig.4, is the scale of a fossilcycloidianfish.

Fins of Fishes.â€”As the progression of fishes through the water is principally effected by the action of the tail, they have no limbs commonly so called. The instruments for balancing the body, and for assisting progression, are the fins, which are composed of numerous rays that support a membranous expansion; and the number and situation of the fins present various modifications in the different orders and genera.

The fins are named according to the situation they occupy; for example,pectoral, those on each side of the chest, and which correspond to the anterior extremities of other vertebrated animals;dorsal, on the back;ventral, on the belly;caudal, on the tail. (See outlines of Fish,Ligns.186,187,195.) The rays are of two kinds; 1st, theSpinousrays; these consist of a single osseous piece, usually dense and pointed, sometimes flexible and elastic, and divided longitudinally (Ligns.188,196); 2d,Softorarticulatedrays, which are composed of numerous small articulations or joints, and divide into branches at their extremities. Many species of fishes have four fins; others six; some but two; and in certain genera they are altogether wanting. In a fossil state the fins are often beautifully preserved; even the soft rays in many of the Tertiary marls and in the Chalk, are found entire, and attached to the body in their natural situation. The large, strong, spinous rays of the dorsal fins of the cartilaginous fishes, as theSharksandRays, are generally found detached, or connected only with a few vertebrÃ¦; but they are so abundant in some of the Secondary deposits (and in numerous instances they are the only vestiges of extinct species and genera), that they possess great geological interest; they are distinguished by the termIchthyodorulites(fossil fish-weapons), under which head they will hereafter be described (seeLign.188). The first ray in the dorsal fin of some fishes is protected in front by a doublerow of enamelled scales, and these often occur in a fossil state (seeLign.196,fig.5).

Teeth of Fishes.â€”Of all the durable parts of animals teeth occur in the mineral kingdom, the teeth of fishes present by far the most numerous, varied, and striking modifications of form, structure, composition, mode of arrangement, and attachment; and yet these dental organs, separately considered, do not in many instances, either in their structure or mode of implantation, afford characters by which the natural affinities of the original can be satisfactorily ascertained; and without the aid of other parts of the skeleton it is often impossible to determine, from external characters only, whether an unknown form of tooth belonged to an animal of the class of Fishes or of Reptiles. Although the modifications of form are almost innumerable, they are referable to four principal types; namely, the conical, the flattened, the prismatic, and the cylindrical.[508]

[508]The "Odontography" of Professor Owen should be consulted by those who would thoroughly comprehend this interesting department of science. See also theArticleTeeth, by Prof. Owen in the CyclopÃ¦dia of Anatomy and Physiology.

The conical teeth are extremely variable in size and form; some are slender, almost invisible points, distributed like the pile of velvet (villous-teeth), or set like the hairs of a brush (brush-teeth); some are long and slender, or barbed at the point; others are obtuse; and many are long and striated at the base, and closely resemble the teeth of certain reptiles. The depressed teeth are equally diversified; some have the grinding surface smooth; others, deeply grooved; in some it is flat; in others convex. In form they are either lozenge-shaped, elliptical, square, oblong, semilunar, &c. The cylindrical teeth are hemispherical, or flattened; in some fishes they are short and thick; in others slender and support an obtuse, conical crown. The prismatic formis equally modified; from the compressed, sharp, lanceolate, cutting teeth, to the strong, triangular, three-pointed dentary organs.[509]

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