CHAPTER V.

PLATE IV.

Of these ancient families, theOsteolepis, or bony-scale, (seePlate IV., fig. 1,) may be regarded as illustrative of the general type. It was one of the first discovered of the Caithness fishes, and received its name in the days of Cuvier, from the osseous character of its scales, ere it was ascertained that it had numerous contemporaries, and that to all and each of these the same description applied. The scales of the fishes of the Lower Old Red Sandstone, like the plates and detached prickles of the purely cartilaginous fishes, were composed of a bony, not of a horny, substance, and were all coated externally with enamel. The circumstance is one of interest.

Agassiz, in his system of classification, has divided fishes into four orders, according to the form of their scales; and his principle of division, though apparently arbitrary and trivial, is yet found to separate the class into great natural families, distinguished from one another by other and very striking peculiarities. One kind of scale, for instance, the placoid or broad-plated scale, is found to characterize all the cartilaginous fishes of Cuvier except the sturgeon;—it is the characteristic of an otherwise well-marked series, whose families are furnished with skeletons composed of mere animal matter, and whose gills open to the water by spiracles. The fish of another order are covered by ctenoid or comb-shaped scales, the posterior margin of each scale being toothed somewhat like the edge of a saw or comb; and the order, thus distinguished, is found wonderfully to agree with an order formed previously on another principle of classification, the Acanthopterygii, or thorny-finned order of Cuvier, excluding only the smooth-scaled families of this previously formed division, and including, in addition to it, the flat fish. A third order, the Cycloidean, is marked by simple marginated scales, like those of the cod, haddock, whiting, herring, salmon, &c.; and this order is found to embrace chiefly theMalacopterygii, or soft-finned order of Cuvier—an order to which all these well-known fish, with an immense multitude of others, belong. Thus the results of the principle of classification adopted by Agassiz wonderfully agree with the results of the less simple principles adopted by Cuvier and the other masters in this department of Natural History. Now, it is peculiar to yet a fourth order, the Ganoidean, or shining-scaled order, that by much the greater number of the genera which it comprises exist only in the fossil state. At least five sixths of the whole were ascertained to be extinct several years ago, at a time when the knowledge of fossil Ichthyology was much more limited than at present: the proportions are now found to be immensely greater on the side of the dead. And this order seems to have included all the semi-osseous, semi-cartilaginous ichthyolites of the Lower Old Red Sandstone: the enamelled scale is the characteristic, according to Agassiz's principle of classification, of the existences that filled the gap so often alluded to as existing in the present creation. All their scales glitter with enamel: they bore to this order the relation that the cartilaginous fish bear to the Placoidean order, the thorny-finned fish to the Ctenoidean order, and the soft-finned fish to the Cycloidean order. It also included, with the semi-cartilaginous, the sauroid fish—those master existences and tyrants of the earlier vertebrata; and both classes find their representatives among the comparatively few ganoid fishes of the present creation; the one in the sturgeon family, which of all existing families approaches nearest in other respects to the extinct semi-cartilaginous fishes; the other in the sauroid genusLepidosteus, to which the bony pike belongs. The head, back, and sides of the sturgeon are defended, as has been already remarked, by longitudinal rows of hard osseous bosses—the bony pike isarmed with enamelled osseous scales, of a stony hardness. It seems a somewhat curious circumstance, that fishes so unlike each other in their internal framework should thus resemble one another in their bony coverings, and in some slight degree in their structure of tail. One of the characteristics of sauroid fishes is the extreme compactness and hardness of their skeleton.[S]

[S]"The sauroid or lizard-like fishes," says Dr. Buckland, "combine in the structure, both of the bones and some of the soft parts, characters which are common to the class of reptiles. The bones of the skull are united by closer sutures than those of common fishes. The vertebræ articulate with the spinous processes of sutures, like the vertebræ of saurians; the ribs also articulate with the extremities of the spinous process. The caudal vertebræ have distinct chevron bones, and the general condition of the skeleton is stronger and more solid than in other fishes: the air bladder also is bifid and cellular, approaching to the character of lungs; and in the throat there is a glottis, as in sirens and salamanders, and many saurians."—Note toBridgewater Treatise, p. 274, first edit.

It requires skill such as that possessed by Agassiz, to determine that the uncouthCoccosteus, or the equally uncouthPterichthys, of the Old Red Sandstone, with their long articulated tails and tortoise-like plates, werebona fidefishes; but there is no possibility of mistaking theOsteolepis: it is obvious to the least practised eye that it must have been a fish, and a handsome one. Even a cursory examination, however, shows very striking peculiarities, which are found, on further examination, to characterize not this family alone, but at least one half the contemporary families besides. We are accustomed to see vertebrated animals with the bone uncovered in one part only,—that part the teeth,—and with the rest of the skeleton wrapped up in flesh and skin. Among the reptiles, we find a few exceptions;but a creature with a skull as naked as its teeth,—the bone being merely covered, as in these, by a hard, shining enamel,—and with toes also of bare enamelled bone, would be deemed an anomaly in creation. And yet such was the condition of theOsteolepis, and many of its contemporaries. The enamelled teeth were placed in jaws which presented outside a surface as naked and as finely enamelled as their own. (SeePlate IV., fig. 5.) The entire head was covered with enamelled osseous plates, furnished inside like other bones, as shown by their cellular construction, with their nourishing blood vessels, and perhaps their oil, and which rested apparently on the cartilaginous box, which must have enclosed the brain, and connected it with the vertebral column. I cannot better illustrate the peculiar condition of the fins of this ichthyolite than by the webbed foot of a water-fowl. The web or membrane in all the aquatic birds with which we are acquainted not only connects, but also covers the toes. The web or membrane in the fins of existing fishes accomplishes a similar purpose; it both connects and covers the supporting bones or rays. Imagine, however, a webbed foot in which the toes—connected, but not covered—present, as in skeletons, an upper and under surface of naked bone; and a very correct idea may be formed, from such a foot, of the condition of fin which obtained among at least one half the ichthyolites of the Lower Old Red Sandstone. The supporting bones or rays seem to have been connected laterally by the membrane; but on both sides they presented bony and finely enamelled surfaces. (SeePlate IV., fig. 6.) In this singular class of fish, all was bone without, and all was cartilage within; and the bone in every instance, whether in the form of jaws or of plates, of scales or of rays, presented an external surface of enamel.

The fins are quite a study. I have alluded to the connecting membrane. In existing fish this membrane is the principal agent in propelling the creature; it strikes against the water, as the membrane of the bat's wing strikes against the air; and the internal skeleton serves but to support and stiffen it for this purpose. But in the fin of theOsteolepis, as in those of many of its contemporaries, we find the condition reversed. The rays were so numerous, and lay so thickly, side by side, like feathers in the wing of a bird, that they presented to the water a surface of bone, and the continuous membrane only served to support and bind them together. In the fins of existing fish we find a sort of bat-wing construction; in those of theOsteolepisa sort of bird-wing construction. The rays, to give flexibility to the organ which they compose, were all jointed, as in the soft-finned fish—as in the herring, salmon, and cod, for example; and we find in all the fins the anterior ray rising from the body in the form of an angular scale: it is a strong, bony scale in one of its joints, and a bony ray in the rest. The characteristic is a curious one.

It is again necessary, in pursuing our description, to refer for illustration to the purely cartilaginous fishes. In at least all the higher orders of these, furnished with movable jaws, such as the sturgeon, the ray, and the shark, the mouth is placed far below the snout. The dog-fish and thorn-back are familiar instances. Further, the mouth in bony fishes is movable on both the upper and under side, like the beak of the parrot; in the higher cartilaginous fishes it is movable, as in quadrupeds, on the under side only. In all their orders, too, except in that of the sturgeon, the gills open to the water by detached spiracles, or breathing-holes; but in the sturgeon, as in the osseous fishes, there is a continuous linearopening, shielded by an operculum, or gill-cover. In the Osteolepis the mouth opened below the snout, but not so far below it as in the purely cartilaginous fishes—not farther below it than in many of the osseous ones—than in the genus Aspro, for instance, or than in the genus Polynemus, or in even the haddock or cod. It was thickly furnished with slender and sharply-pointed teeth. I have hitherto been unable fully to determine whether, like the mouths of the osseous fishes, it was movable on both sides; though, from the perfect form of what seems to be the intermaxillary bone, I cannot avoid thinking it was. The gills opened, as in the osseous fishes, in continuous lines, and were covered by large bony opercules—that on the enamelled side somewhat resemble round japanned shields.

But while the head of theOsteolepis, with its appendages, thus resembled, in some points, the heads of the bony fishes, the tail, like those of most of its contemporaries, differed in no respect from the tails of cartilaginous ones, such as the sturgeon. The vertebral column seems to have run on to well nigh the extremity of the caudal fin, which we find developed chiefly on the under side. The tail was a one-sided tail. Take into account with these peculiarities—peculiarities such as the naked skull, jaws, and operculum, the naked and thickly-set rays, and the unequally lobed condition of tail—a body covered with scales, that glitter like sheets of mica, and assume, according to their position, the parallelogramical, rhomboidal, angular, or polygonal form—a lateral line raised, not depressed—a raised bar on the inner or bony side of the scales, which, like the doubled-up end of a tile, seems to have served the purpose of fastening them in their places—a general clustering of alternate fins towards the tail—and thetout ensemblemust surely impart to the reader the idea of a very singular little fish. The ventral fins front the space which occurs between the two dorsals, and the anal fin the space which intervenes between the posterior dorsal fin and the tail. The length of theOsteolepis, in my larger specimens, somewhat exceeds a foot; in the smaller, it falls short of six inches. There exist at least three species of this ichthyolite, distinguished chiefly, in two of the instances, by the smaller and larger size of their scales, compared with the bulk of their bodies, and by punctulated markings on the enamel in the case of the third. This last, however, is no specific difference, but common to the entire genus, and to several other genera besides. The names are,Osteolepis macrolepidotus,O. microlepidotus, andO. arenatus.[T]

[T]To these there have since been addedOsteolepis major,O. intermedius, andO. nanus; the two latter, however, Agassiz regards as doubtful.

PLATE V.

Next to theOsteolepiswe may place theDipterus, or double-wing, of the Lower Old Red Sandstone, an ichthyolite first introduced to the knowledge of geologists by Mr. Murchison, who, with his friend, Mr. Sedgwick, figured and described it in a masterly paper on the older sedimentary formations of the north of Scotland, which appeared in theTransactions of the Geological Society of Londonfor 1828. The name, derived from its two dorsals, would suit equally well, like that of the Osteolepis, many of its more recently discovered contemporaries. From the latter ichthyolite it differed chiefly in the position of its fins, which were opposite, not alternate; the double dorsals exactly fronting the anal and ventral fins. (SeePlate V., fig. 1.) TheDiplopterus, a nearly resembling ichthyolite of the same formation, also owes its name to the order and arrangement of its fins,which, like those of theDipterus, were placed fronting each other, and in pairs. But the head, in proportion to the body, was in greater size than in either theDipterusorOsteolepis; and the mouth, as indicated by the creature's length of jaw, must have been of much greater width. In their more striking characteristics, however, the three genera seem to have nearly agreed. In all alike, scales of bone glisten with enamel; their jaws, enamel without and bone within, bristle thick with sharp-pointed teeth; closely-jointed plates, burnished like ancient helmets, cover their heads, and seem to have formed a kind of outer table to skulls externally of bone and internally of cartilage; their gill-covers consist each of a single piece, like the gill-cover of the sturgeon; their tails were formed chiefly on the lower side of their bodies; and the rays of their fins, enamelled like their plates and their scales, stand up over the connecting membrane, like the steel or brass in that peculiar armor of the middle ages, whose multitudinous pieces of metal were fastened together on a groundwork of cloth or of leather. All their scales, plates, and rays present a similar style of ornament. The shining and polished enamel is mottled with thickly-set punctures, or, rather, punctulated markings; so that a scale or plate, when viewed through a microscope, reminds one of the cover of a saddle. Some of the ganoid scales of Burdie House present surfaces similarly punctulated.[U]

[U]There exists, according to Agassiz, only a single species ofDipterus—D. macrelepidotus; whereas four species ofDiplopterushave been enumerated—D. affinis,D. borealis,D. macrocephalus, andD. Agassizii. The existence of the last named, however, as a distinct species, is regarded as problematical by the distinguished naturalist whose name has been affixed to it.

TheGlyptolepis, or carved scale, may be regarded as the representative of a family of the Lower Old Red Sandstone, which, differing very materially from the genera described, had yet many traits in common with them, such as the bare, bony skull, the bony scales, the naked rays, and the unequally sided condition of tail. The fins, which were of considerable length in proportion to their breadth of base, and present in some of the specimens a pendulous-like appearance, cluster thick together towards the creature's lower extremities, leaving the upper portion bare. There are two dorsals placed as in theDipterusandDiplopterus—the anterior directly opposite the ventral fin, the posterior directly opposite the anal. The tail is long and spreading;—the rays, long and numerously articulated, are comparatively stout at their base, and slender as hairs where they terminate. The shoulder-bones are of huge dimensions, the teeth extremely minute. But the most characteristic parts of the creature are the scales. They are of great size, compared with the size of the animal. An individual not more than half a foot in length, the specimen figured, (seePlate V., fig. 2,) exhibits scales fully three eighth parts of an inch in diameter. In another more broken specimen there are scales a full inch across, and yet the length of the ichthyolite to which they belonged seems not to have much exceeded a foot and a half. Each scale consists of a double plate, an inner and an outer. The structure of the inner is not peculiar to the family or the formation: it is formed of a number of minute concentric circles, crossed by still minuter radiating lines—the one described, and the other proceeding from a common centre. (SeePlate V., fig. 5.) All scales that receive their accessions of growth equally at their edges exhibit, internally, a corresponding character. The outer plate presents an appearance lesscommon. It seems relieved into ridges that drop adown it like sculptured threads, some of them entire, some broken, some straight, some slightly waved, (seePlate V., fig. 3;) and hence the name of the ichthyolite. The plates of the head were ornamented in a similar style, but their threads are so broken as to present the appearance of dotted lines, the dots all standing out in bold relief. My collection contains three varieties of this family; one of them disinterred from out the Cromarty beds about seven years ago, and the others only a little later, though partly from the inadequacy of a written description, through which I was led to confound theOsteolepiswith theDiplopterus, and to regard theGlyptolepisas theOsteolepis, I was not aware until lately that the discovery was really such; and under the latter name I described the creature in the Witness newspaper several weeks ere it had received the name which it now bears. It was first introduced to the notice of Agassiz, in Autumn last, by Lady Cumming of Altyre. The species, however, was a different one from any yet found at Cromarty.[V]

[V]There are three species ofGlyptolepis—G. elegans,G. Leptopterus, andG. microlepidotus.

TheCheirolepis, or scaly pectoral, forms the representative of yet another family of the Lower Old Red Sandstone, and one which any eye, however unpractised, could at once distinguish from the families just described. Professor Traill of the University of Edinburgh, a gentleman whose researches in Natural History have materially extended the boundaries of knowledge, and whose frankness in communicating information is only equalled by his facility in acquiring it, was the first discoverer of this family, one variety of which, theCheirolepis Traillii, bears his name. The figured specimen(Plate VI., fig. 1) Agassiz has pronounced a new species, the discovery of the writer. In all the remains of this curious fish which I have hitherto seen, the union of the osseous with the cartilaginous, in the general framework of the creature, is strikingly apparent. The external skull, the great shoulder-bone, and the rays of the fins, are all unequivocally osseous; the occipital and shoulder-bones, in particular, seem of great strength and massiveness, and are invariably preserved, however imperfect the specimen in other respects; whereas, even in specimens the most complete, and which exhibit every scale and every ray, however minute, and show unchanged the entire outline of the animal, not a fragment of the internal skeleton appears. TheCheirolepisseems to have varied from fourteen to four inches in length. When seen in profile, the under line, as in the figured variety, seems thickly covered with fins, and the upper line well nigh naked. The large pectorals almost encroach on the ventral fins, and the ventrals on the anal fin; whereas the back, for two thirds the entire length of the creature, presents a bare rectilinear ridge, and the single dorsal, which rises but a little way over the tail, immediately opposite the posterior portion of the anal fin, is comparatively of small size. The tail, which, in the general condition of being developed chiefly on the lower side, resembles the tails of all the creature's contemporaries, is elegantly lobed. The scales, in proportion to the bulk of the body which they cover, are not more than one twentieth the size of those of theOsteolepis. They are richly enamelled, and range diagonally from the shoulder to the belly in waving lines; and so fretted is each individual scale by longitudinal grooves and ridges, that, on first bringing it under the glass, it seems a little bunch of glittering thorns, though, when more minutely examined, it isfound to be present somewhat the appearance of the outer side of the deep-sea cockle, with its strongly marked ribs and channels, the point in which the posterior point terminates representing the hinge. (SeePlate VI., fig. 2.) The bones of the head, enamelled like the scales, are carved into jagged inequalities, somewhat resembling those on the skin of the shark, but more irregular. The sculpturings seem intended evidently for effect. To produce harmony of appearance between the scaly coat and the enamelled occipital plates of bone, the surfaces of the latter are relieved, where they border on the shoulders, into what seem scales, just as the dead walls of a building are sometimes, for the sake of uniformity, wrought into blind windows. The enamelled rays of the fins are finished, if I may so speak, after the same style. They lie thick upon one another as the fibres of a quill, and like these, too, they are imbricated on the sides, so that the edge of each seems jagged into a row of prickles. (SeePlate VI., fig. 3.) The jaws of the Cheirolepis were armed with thickly-set sharp teeth, like those of its contemporaries, theOsteolepisandDiplopterus.[W]

[W]There have been five species ofCheirolepisenumerated—C. Cummingiæ,C. splendens,C. Traillii,C. unilateralisandC. Uragus. TheCheirolepis splendensandC. unilateralisAgassiz regards as doubtful.

PLATE VI.

The Classifying Principle, and its Uses.—Three groups of Ichthyolites among the Organisms of the Lower Old Red Sandstone.—Peculiarities of the Third Group.—Its Varieties.—Description of the Cheiracanthus.—Of two unnamed Fossils of the same Order.—Microscopic Beauty of these Ancient Fish.—Various Styles of Ornament which obtain among them.—The Molluscs of the Formation.—Remarkable chiefly for the Union of Modern with Ancient Forms which they exhibit.—Its Vegetables.—Importance and Interest of the Record which it furnishes.

There rests in the neighborhood of Cromarty, on the upper stratum of one of the richest ichthyolite beds I have yet seen, a huge water-rolled boulder of granitic gneiss, which must have been a traveller, in some of the later periods of geological change, from a mountain range in the interior highlands of Ross-shire, more than sixty miles away. It is an uncouth looking mass, several tons in weight, with a flat upper surface, like that of a table; and as a table, when engaged in collecting my specimens, I have often found occasion to employ it. I have covered it over, times without number, with fragments of fossil fish—with plates, and scales, and jaws, and fins, and, when the search proved successful, with entire ichthyolites. Why did I always arrange them, almost without thinking of the matter, into three groups? Why, even when the mind was otherwise employed, did the fragments of theCoccosteusandPterichthyscome to occupy one corner of the stone, and those of the various fish just described another corner, and the equally well-marked remains of a yet different division a third corner? Theprocess seemed almost mechanical, so little did it employ the attention, and so invariable were the results. The fossils of the surrounding bed always found their places on the huge stone in three groups, and at times there was yet a fourth group added—a group whose organisms belonged not to the animal, but the vegetable kingdom. What led to the arrangement, or in what did it originate? In a principle inherent in the human mind—that principle of classification which we find pervading all science—which gives to each of the many cells of recollection its appropriate facts—and without which all knowledge would exist as a disorderly and shapeless mass, too huge for the memory to grasp, and too heterogeneous for the understanding to employ. I have described but two of the groups, and must now say a very little about the principle on which, justly or otherwise, I used to separate the third, and on the distinctive differences which rendered the separation so easy.

The recent bony fishes are divided, according to the Cuvierian system of classification, into two great orders, the soft-finned and the thorny-finned order—theMalacopterygiiand theAcanthopterygii. In the former the rays of the fins are thin, flexible, articulated, branched: each ray somewhat resembles a jointed bamboo; with this difference, however, that what seems a single ray at bottom, branches out into three or four rays a-top. In the latter, (the thorny-finned order,)—especially in their anterior dorsal, and perhaps anal fins,—the rays are stiff continuous spikes of bone, and each stands detached as a spear, without joint or branch. The perch may be instanced as a familiar illustration of this order—the gold-fish of the other. Now, between the fins of two sets—shall I venture to say orders?—of the ichthyolites of the Lower Old Red Sandstone, an equally striking differenceobtains. The fin of theOsteolepis, with its surface of enamelled and minutely jointed bones, I have already described as a sort of bird-wing fin. The naked rays, with their flattened surfaces, lay thick together as feathers in the wing of a bird—so thick as to conceal the connecting membrane; and fins of similar construction characterized the families of theDipterus,Diplopterus,Glyptolepis,Cheirolepis,Holoptychius, and, I doubt not, many other families of the same period, which await the researches of future discoverers. But the fins of another set of ichthyolites, their contemporaries, may be described as bat-wing fins: they presented to the water a broad expanse of membrane; and the solitary ray which survives in each was not a jointed, but a continuous spear-like ray. The fins of this set, or order, are thorny-fins, like those of theAcanthopterygii; the anterior edge of each, with the exception of, perhaps, the caudal fin, which differs in construction from the others, is composed of a strong, bony spike. Such, with some tacit reference, perhaps, to the similar Cuvierian principle of classification, were the distinctive differences, on the strength of which I used to arrange two of my groups of fossils on the granitic boulder; and the influence of the same principle, almost instinctively exerted,—for, in writing the previous pages, I scarce thought of its existence,—has, I find, given to each group its own chapter.

Of the membranous-finned and thorny-rayed order of ichthyolites, theCheiracanthus, or thorny-hand, (i. e.pectoral,) may be regarded as an adequate representative. (SeePlate VII., fig. 1.) TheCheiracanthusmust have been an eminently handsome little fish—slim, tapering, and described in all its outlines, whether of the body or the fins, by gracefully waved lines. It is, however, a rare matter to find it presenting its original profile in the stone;—none of the other ichthyolitesare so frequently distorted as theCheiracanthus. It seems to have been more a cartilaginous and less an osseous fish than most of its contemporaries. However perfect the specimen, no part of the internal skeleton is ever found, not even when scales as minute as the point of a pin are preserved, and every spine stands up in its original place. And hence, perhaps, a greater degree of flexibility, and consequent distortion. The body was covered with small angular scales, brightly enamelled, and delicately fretted into parallel ridges, that run longitudinally along the upper half of the scale, and leave the posterior portion of it a smooth, glittering surface. (SeePlate VII., fig. 2.) They diminish in size towards the head, which, from the faint stain left on the stone, seems to have been composed of cartilage exclusively, and either covered with skin, or with scales of extreme minuteness. The lower edge of the operculum bears a tagged fringe, like that of a curtain. The tail, a fin of considerable power, had the unequal sided character common to the formation; and the slender and numerous rays on both sides are separated by so many articulations as to present the appearance of parallelogramical scales. The other fins are comparatively of small size. There is a single dorsal placed about two thirds the entire length of the creature adown the back; and exactly opposite its posterior edge is the anterior edge of the anal fin. The ventral fins are placed high upon the belly, somewhat like those of the perch; the pectorals only a little higher. But it is rather in the construction of the fins, than their position, that the peculiarities of theCheiracanthusare most marked. The anterior edge of each, as in the pectorals of the existing generaCestracionandChimæra, is formed of a strong, large spine. In theChimæra borealis, a cartilaginous fish of the Northern Ocean, the spine seems placed in front of the weaker rays, just, if I may be allowed the comparison, as, in a line of mountaineers engaged in crossing a swollen torrent, the strongest man in the party is placed on the upper side of the line, to break off the force of the current from the rest. In theCheiracanthus, however, each fin seems to consist of but a single spine, with an angular membrane fixed to it by one of its sides, and attached to the creature's body on the other. Its fins are masts and sails—the spine representing the mast, and the membrane the sail; and it is a curious characteristic of the order, that the membrane, like the body, of the ichthyolite, is thickly covered with minute scales. The mouth seems to have opened a very little under the snout, as in the haddock; and there are no indications of its having been furnished with teeth.[X]

[X]There have been three species ofCheiracanthusdetermined—C. microlepidotus,C. minor, andC. Murchisoni.

PLATE VII.

An ichthyolite first discovered by the writer about three years ago, and introduced by him to the notice of Agassiz during his recent visit to Edinburgh, but still unfurnished with a name,[Y]is a still more striking representative of this order than even theCheiracanthus. It must have been proportionally thick and short, like some of the tropical fishes, though rather handsome than otherwise. (SeePlate VIII., fig. 1.) The scales, minute, but considerably larger than those of theCheiracanthus, are of a rhomboidal form, and so regularly striated—the striæ converging to a point at the posterior termination of each scale—that, when examined with a glass, the body appears as if covered with scallops. (See PlateVIII., fig. 3.) It seems a piece of exquisite shell-work, such as we sometimes see on the walls of a grotto. There are two dorsals—the posterior, immediately over the tail, and directly opposite the anal fin; the anterior, somewhat higher up than the ventrals; and all the fins are of great size. The anterior edge of each is formed of a strong spine, round as the handle of a halbert, and diminishing gradually and symmetrically to a sharp point. Though formed externally of solid bone, it seems to have been composed internally of cartilage, like the bones of some of the osseous fishes—those of the halibut, for instance; and the place of the cartilage is generally occupied in the stone by carbonate of lime. The membrane which formed the body of the fin was covered, like that of theCheiracanthus, with minute scales, of the same scallop-like pattern with the rest, but of not more than one sixth the size of those which cover the creature's sides and back. Imagine two lug-sails stiffly extended between the deck of a brigantine and her two masts, the latter raking as far aft as to form an angle of sixty degrees with the horizon, and some idea may be formed of the dorsals of this singular fish. They were lug-sails, formed not to be acted upon by the air, but to act upon the water. None of my specimens show the head; but, judging from analogies furnished by the other families of the group, I entertain little doubt that it will be found to be covered, not by bony plates, but by minute scales, diminishing, as they approach the snout, into mere points. In none of the specimens does any part of the internal skeleton survive.

[Y]Now determined to be a species ofDiplacanthus—D. longispinus.

PLATE VIII.

My collection contains the remains of yet another fish of this group, which was unfurnished with a name only a few months ago, but which I first discovered about five years since. (SeePlate VIII., fig. 2.) It is now designated theDiplacanthus; and, though the smallest ichthyolite of the formation yet known, it is by no means the least curious. The length from head to tail, in some of my specimens, does not exceed three inches; the largest fall a little short of five. The scales, which are of such extreme minuteness that their peculiarities can be detected by only a powerful glass, resemble those of theCheiracanthus; but the ridges are more waved, and seem, instead of running in nearly parallel lines, to converge towards the apex. There are two dorsals, the one rising immediately from the shoulder, a little below the nape, the other directly opposite the anal fin. The ventrals are placed near the middle of the belly. There is a curious mechanism of shoulder-bone involved with a lateral spine and with the pectorals. The creature, unlike theCheiracanthus, seems to have been furnished with jaws of bone: there are fragments of bone upon the head, tubercled apparently on the outer surface; and minute cylinders of carbonate of lime running along all the larger bones, where we find them accidentally laid open, show that they were formed on internal bases of cartilage. But the best marked characteristic of the creature is furnished by the spines of its fins, which are of singular beauty. Each spine resembles a bundle of rods, or, rather, like a Gothic column, the sculptured semblance of a bundle of rods, which finely diminish towards a point, sharp and tapering as that of a rush. (SeePlate VIII., fig. 4.)[Z]The rest of the fin presents the appearance of a mere scaly membrane, and no part of the internal skeleton appears. Perhaps this last circumstance, common to all the ichthyolites of the formation, if we except the families of theCoccosteusandPterichthys, may throw some light on the apparently membranous condition of fin peculiar to the families of this order. What appears in the fossil a mere scaly membrane attached to a single spine of bone, may have had in the living animal a cartilaginous framework, like the fins of the dog-fish and thorn-back, that are amply furnished with rays of cartilage—though, of course, all such rays must have disappeared in the stone, like the rest of the internal skeleton. Unquestionably, the caudal fin of the two last described fossils must have been strengthened by some such internal framework; for, as they differ from the other fins, in being unprovided with osseous spines, they would have formed, without an internal skeleton, mere pendulous attachments, altogether unfitted to serve the purposes of instruments of motion. There may be found in the bony spines of all this order direct proof that, had there been an internal skeleton of bone, it would have survived. The spines run deep into the body, as a ship's masts run deep into her hulk; and we can see them standing up among the scales to their termination, in such bold relief, that, from a sort of pictorial illusion, they seem as if fixed to the creature's sides, and foreshortened, instead of rising in profile from its back or belly. (SeePlate VIII., fig. 1.) The observer will of course remember, that, in the living animal, the view of the spine must have terminated with the line of the profile, just as the view of a vessel's mast terminates with the deck, though the mast itself penetrates to the interior keel. Now, it must be deemed equally obvious, that, had the vertebral column been of bone, not of cartilage, instead of exhibiting no trace, even the faintest, of having ever existed, it would have stood out in as high relief as the internal buts or stocks of the spines. And such are the general characteristics of a few of the ichthyolites of thislower formation of the Old Red Sandstone—a few of the more striking forms, sculptured, if I may so speak, on the middle compartment of the Caithness pyramid. It would be easy rendering the list more complete at even the present stage, when the field is still so new that almost every laborer in it can exhibit genera and species unknown to his brother laborers. The remains of a species ofHoloptychiushave been discovered low in the formation, at Orkney, by Dr. Traill; similar remains have been found in it at Gamrie. In its upper beds the specimens seem so different from those in the lower, that, in extensive collections made from the inferior strata of one locality, Agassiz has been unable to identify a single specimen with the specimens of collections made from the superior strata of another, though the genera are the same. Meanwhile there are heads and hands at work on the subject; Geology has become a Briareus; and I have little doubt that, in five years hence, this third portion of the Old Red Sandstone will be found to contain as many distinct varieties of fossil fish as the whole geological scale was known to contain fifteen years ago.[AA]

[Z]Agassiz reckons four species ofDiplacanthus—D. crassispinus,D. longispinus,D. striatulus, andD. striatus.

[AA]This prediction has been already more than accomplished. At the death of Cuvier, in 1832, there were but ninety-two species of fossil fish known to the geologist; Agassiz now enumerates one hundred and five species that belong to the Old Red Sandstone alone; and if we include doubtful species, on which he has not authoritatively decided—some of which, however, were included in the list of Cuvier—one hundred and fifty-one.

There is something very admirable in the consistency of style which obtains among the ichthyolites of this formation. In no single fish of either group do we find two styles of ornament—in scarce any two fishes do we find exactly the same style. I pass fine buildings almost every day. In somethere is a discordant jumbling—an Egyptian Sphinx, for instance, placed over a Doric portico; in all there prevails a vast amount of timid imitation. The one repeats the other, either in general outline or in the subordinate parts. But the case is otherwise among the ichthyolites of the Old Red Sandstone; nor does it lessen the wonder, that their nicer ornaments should yield their beauty only to the microscope. There is unity of character in every scale, plate, and fin—unity such as all men of taste have learned to admire in those three Grecian orders from which the ingenuity of Rome was content to borrow, when it professed to invent—in the masculine Doric, the chaste and graceful Ionic, the exquisitely elegant Corinthian; and yet the unassisted eye fails to discover the finer evidences of this unity: it would seem as if the adorable Architect had wrought it out in secret with reference to the Divine idea alone. The artist who sculptured the cherry-stone consigned it to a cabinet, and placed a microscope beside it; the microscopic beauty of these ancient fish was consigned to the twilight depths of a primeval ocean. There is a feeling which at times grows upon the painter and the statuary, as if the perception and love of the beautiful had been sublimed into a kind of moral sense. Art comes to be pursued for its own sake; the exquisite conception in the mind, or the elegant and elaborate model, becomes all in all to the worker, and the dread of criticism or the appetite of praise almost nothing. And thus, through the influence of a power somewhat akin to conscience, but whose province is not the just and the good, but the fair, the refined, the exquisite, have works prosecuted in solitude, and never intended for the world, been found fraught with loveliness. Sir Thomas Lawrence, when finishing, with the most consummate care, a picture intended for a semi-barbarous, foreigncourt, was asked why he took so much pains with a piece destined, perhaps, never to come under the eye of a connoisseur. "I cannot help it," he replied; "I do the best I can, unable, through a tyrant feeling, that will not brook offence, to do any thing less." It would be perhaps over bold to attribute any such overmastering feeling to the Creator; yet certain it is, that among his creatures well nigh all approximations towards perfection, in the province in which it expatiates, owe their origin to it, and that Deity in all his works is his own rule.

TheOsteolepiswas cased, I have said, from head to tail, in complete armor. The head had its plaited mail, the body its scaly mail, the fins their mail of parallel and jointed bars; the entire suit glittered with enamel; and every plate, bar, and scale was dotted with microscopic points. Every ray had its double or treble punctulated row, every scale or plate its punctulated group; the markings lie as thickly in proportion to the fields they cover, as the circular perforations in a lace veil; and the effect, viewed through the glass, is one of lightness and beauty. In theCheirolepisan entirely different style obtains. The enamelled scales and plates glitter with minute ridges, that show like thorns in a December morning varnished with ice. Every ray of the fins presents its serrated edge, every occipital plate and bone its sculptured prominences, every scale its bunch of prickle-like ridges. A more rustic style characterized theGlyptolepis. The enamel of the scales and plates is less bright; the sculpturings are executed on a larger scale, and more rudely finished. The relieved ridges, waved enough to give them a pendulous appearance, drop adown the head and body. The rays of the fins, of great length, present also a pendulous appearance. The bones and scales seem disproportionately large.There is a general rudeness in the finish of the creature, if I may so speak, that reminds one of the tattooings of a savage, or the corresponding style of art in which he ornaments the handle of his stone-hatchet or his war-club. In theCheiracanthus, on the contrary, there is much of a minute and cabinet-like elegance. The silvery smoothness of the fins, dotted with scarcely visible scales, harmonized with a similar appearance of head; a style of sculpture resembling the parallel etchings of the line-engraver fretted the scales; the fins were small, and the contour elegant. I have already described the appearance of the unnamed fossils—the seeming shell-work that covered the sides of the one—its mast-like spines and sail-like fins; and the Gothic-like peculiarities that characterized the other—its rodded, obelisk-like spines, and the external framework of bone that stretched along its pectorals.

Till very lately, it was held that the Old Red Sandstone of Scotland contained no mollusca. It seemed difficult, however, to imagine a sea abounding in fish, and yet devoid of shells. In all my explorations, therefore, I had an eye to the discovery of the latter, and on two several occasions I disinterred what I supposed might have formed portions of a cardium or terebratula. On applying the glass, however, the punctulated character of the surface showed that the supposed shells were but parts of the concave helmet-like plate that covered the snout of theOsteolepis. In the ichthyolite beds of Cromarty and Ross, of Moray, Banff, Perth, Forfar, Fife, and Berwickshire, not a single shell has yet been found; but there have been discovered of late, in the upper beds of the Lower Old Red Sandstone in Orkney, the remains of a small, delicate bivalve, not yet described or figured, but which very much resembles aVenus. (SeePlate V., fig. 7.) In the Tilestonesof England, so carefully described by Mr. Murchison in hisSilurian System, shells are very abundant; and the fact may now be regarded as established, that the Tilestones of England belong to a deposit contemporaneous with the ichthyolite beds of Caithness and Cromarty. They occupy the same place low in the base of the Old Red; and there is at least one ichthyolite common to both,[AB]and which does not occur in the superior strata of the system in either country—theDipterus macrolepidotus. The evidence that the fish and shells lived in the same period, and represent, therefore, the same formation, may be summed up in a single sentence. We learn from the Geology of Caithness that this species ofDipteruswas unquestionably contemporary with all the other ichthyolites described;—we learn from the Geology of Herefordshire that the shells were as unquestionably contemporary with it.[AC]These—the shells—are of a singularly mixed character, regarded as a group, uniting, says Mr. Murchison, forms at one time deemed characteristic of the more modern formations,—of the latter secondary, and even tertiary periods,—with forms the most ancient, and which characterize the molluscous remains of the transition rocks. Turbinated shells and bivalves of well nigh the recent type may be found lying side by side with chambered Orthoceratites and Terebratula.[AD]

Back to Index Next