It must be obvious that another and most important branch of natural history is enlisted in aid of Geology, as soon as the study of the character of fossil Fishes has been established on any footing, which admits of such general application as the system now proposed. We introduce an additional element into geological calculations; we bring an engine of great power, hitherto unapplied, to bear on the field of our inquiry, and seem almost to add a new sense to our powers of geological perception. The general result is, that fossil Fishes approximate nearest to existing genera and species, in the most recent Tertiary deposits; and differ from them most widely in strata whose antiquity is the highest; and that strata of intermediate age are marked by intermediate changes of ichthyological condition.

are well known, from the use made of them in rasping and polishing wood, and for shagreen.

Second Order, GANOIDIANS. (Pl. 27, 3, 4. Etym. gavos, splendour, from the bright surface of their enamel.) The families of this Order are characterized by angular scales, composed of horny or bony plates, covered with a thick plate of enamel. The bony Pike (Lepidosteus Osseus, Pl. 27a, Fig. 1;) and Sturgeons are of this Order. It contains more than sixty genera, of which fifty are extinct.

Third Order, CTENOIDIANS. (Pl. 27, Figs. 5, 6. Etym. xv, a comb.) The Ctenoidians have their scales jagged or pectinated, like the teeth of a comb, on their posterior margin. They are formed of laminæ of horn or bone, but have no enamel. The Perch affords a familiar example of scales constructed on this principle.

Fourth Order, CYCLOIDIANS. (Pl. 27, Figs. 7, 8. Etym, xuxλos, a circle.) Families of this Order have their scales smooth, and simple at their margin, and often ornamented with various figures on the upper surface: these scales are composed of laminæ of horn or bone, but have no enamel. The Herring and Salmon are examples of Cycloidians.

Each of these Orders contains both cartilaginous and bony Fishes: the representatives of each prevailed in different proportions during different epochs; only the first two existed before the commencement of the Cretaceous formations; the third and fourth Orders, which contain three-fourths of the eight thousand known species of living Fishes, appear for the first time in the Cretaceous strata, when all the preceding fossil genera of the first two Orders had become extinct.

It appears still farther, that all the great changes in the character of fossil Fishes take place simultaneously with the most important alterations in the other classes of fossil animals, and in fossil vegetables; and also in the mineral condition of the strata.*

It is satisfactory to find that these conclusions are in perfect accordance with those to which geologists had arrived from other data. The details that lead to them, will be described by M. Agassiz, in a work of many volumes, and will form a continuation of the Ossemens Fossiles of Cuvier. From the parts of this work already published, and from communications by the author, I select a few examples illustrating the character of some of the most remarkable families of fossil Fishes.

It appears that the character of fossil Fishes does not change insensibly from one formation to another, as in the case of many Zoophytes and Testacea; nor do the same genera, or even the same families, pervade successive series of great formations; but their changes take place abruptly, at certain definite points in the vertical succession of the strata, like the sudden changes that occur in fossil Reptiles and Mammalia.† Not a single species of fossil Fishes has

stone.

* The genera of Fishes which prevail in strata of the Carboniferous order are found no more after the deposition of the Zechstein, or Magnesian limeThose of the Oolitic series were introduced after the Zechstein, and ceased suddenly at the commencement of the Cretaceous formations. The genera of the Cretaceous formations are the first that approximate to existing genera. Those of the lower Tertiary deposites of London, Paris, and Monte Bolca, are still more nearly allied to existing forms; and the fossil Fishes of Oeningen and Aix approximate again yet closer to living genera, although every one of their species appears to be extinct.

+ M. Agassiz observes that fossil Fishes in the same formation present greater variation of species at distant localities, than we find in the species of shells and Zoophytes, in corresponding parts of the same formation; and that this circumstance is readily explained by the greater locomotive powers of this higher class of animals.

yet been found that is common to any two great geological formations; or living in our present seas.*

One important geological result has already attended the researches of M. Agassiz, viz. that the age and place of several formations hitherto unexplained by any other character, have been made clear by a knowledge of the fossil Fishes which they contain.†

Sauroid Fishes in the Order Ganoid.

The voracious family of Sauroid, or Lizard-like Fishes, first claims our attention, and is highly important in the physiological consideration of the history of Fishes, as it

* The nodules of clay stone on the coast of Greenland, containing fishes of a species now living in the adjacent seas, (Mallotus Villosus) are probably modern concretions.

† Thus the slate of Engi, in the canton of Glaris, in Switzerland, has long been one of the most celebrated, and least understood localities of fossil Fishes in Europe, and the mineral character of this slate had till lately caused it to be referred to the early period of the Transition series. M. Agassiz has found that among its numerous fishes, there is not one belonging to a single genus, that occurs in any formation older than the Cretaceous series; but that many of them agree with fossil species found in Bohemia, in the lower Cretaceous formation, or Pläner kalk; hence he infers that the Glaris slate is an altered condition of an argillaceous deposite, subordinate to the great Cretaceous formations of other parts of Europe, probably of the Gault.

Another example of the value of Ichthyology, in illustration of Geology, occurs in the fact, that as the fossil Fishes of the Wealden estuary forma. tion are referable to genera that characterize the strata of the Oolitic series, the Wealden deposites are hereby connected with the Oolitic period that preceded their commencement, and are separated from the Cretaceous formations that followed their termination. A change in the condition of the higher orders of the inhabitants of the waters seems to have accompanied the changes that occurred in the genera and species of inferior animals at the commencement of the Cretaceous formations.

A third example occurs, in the fact that M. Agassiz has, by resemblances in the character of their fossil Fishes, identified the hitherto unknown periods of the fresh-water deposites of Oeningen, and of Aix in Provence, with that of the Molasse of Switzerland.

combines in the structure both of the bones, and some of the soft parts, characters which are common to the class of reptiles. M. Agassiz has already ascertained seventeen genera of Sauroid Fishes. Their only living representatives are the genus Lepidosteus,* or bony Pike (Pl. 27a Fig. 1.) and the genus Polypterus (Agass. Poiss. Foss. Vol. 2. Tab. C.) the former containing five species, and the latter two. Both these genera are found only in fresh-waters, the Lepidosteus in the rivers of North America, and the Polypterus in the Nile, and the waters of Senegal.†

The teeth of the Sauroid Fishes are striated longitudinally towards the base, and have a hollow cone within. (See Pl. 27, 2, 3, 4; and Pl. 27. 9, 10, 11, 12, 13, 14.) The bones of the palate also are furnished with a large apparatus of teeth.

Pl. 27, Figs. 11, 12, 13, 14, represent teeth of the largest Sauroid Fishes yet discovered, equalling in size the teeth of the largest Crocodiles: they occur in the lower region of the coal formation near Edinburgh, and are referred by M. Agassiz to a new genus, Megalichthys. Pl. 27, Fig. 9, and Pl. 27a, Fig. 4, are fragments of jaws, containing many

* Lepidosteus Agassiz-Lepisosteus Lacépède.

The bones of the skull, in Sauroid Fishes, are united by closer sutures than those of common Fishes. The vertebræ articulate with the spinous processes by sutures, like the vertebræ of Saurians; the ribs also articulate with the extremities of the transverse processes. 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.-See Report of Proceedings of Zool. Soc. London, October, 1834.

The object of the extensive apparatus of teeth, over the whole interior of the mouth of many of the most voracious Fishes, appears not to be for mastication, but to enable them to hold fast, and swallow the slippery bodies of other Fishes that form their prey. No one who has handled a living Trout or Eel can fail to appreciate duly the importance of the apparatus in ques tion.

smaller teeth of the same kind. The external form of all these teeth are nearly conical, and within them is a conical cavity, like that within the teeth of many Saurians; their base is fluted, like the base of the teeth of the Ichthyosaurus. Their prodigious size shows the magnitude which Fishes of this family attained at a period so early as that of the Coal formation:* their structure coincides entirely with that of the teeth of the living Lepidosteus osseus. (Pl. 27', Figs. 1, 2, 3.)

Smaller Sauroid Fishes only have been noticed in the

* We owe the discovery of these very curious teeth, and much valuable information on the Geology of the neighbourhood of Edinburgh, to the zeal and discernment of Dr. Hibbert, in the spring of 1834. The limestone in which these Fishes occur lies near the bottom of the Coal formation, and is loaded with Coprolites, derived apparently from predaceous Fishes. It is abundantly charged also with ferns, and other plants of the coal formation; and with the crustaceous remains of Cypris, a genus known only as an inhabitant of fresh-water. These circumstances, and the absence of Corals and Encrinites, and of all species of marine shells, render it probable that this deposite was formed in a fresh-water lake, or estuary. It has been recog nised in various and distant places, at the bottom of the carboniferous strata near Edinburgh.

In the Transactions of the Royal Society of Edinburgh, Vol. XIII. Dr. Hibbert has published a most interesting description of the recent discoveries made in the limestone of Burdie House, illustrated with engravings, from which the larger teeth in our plate are copied. (Pl. 27, Fig. 11, 12, 13, 14.) The smaller figures, Pl. 27, Fig. 9, and Pl. 27a, Fig. 4, are drawn from specimens belonging to Dr. Hibbert and the Royal Society of Edinburgh.

In this memoir, Dr. Hibbert has also published figures of some curious large scales, found at Burdie House, with the teeth of Megalichthys, and referred by M. Agassiz to that Fish. Similar scales have been noticed in various parts of the Edinburgh Coal field, and also in the Coal formation of Newcastle-on-Tyne. Unique specimens of the heads of two similar Fishes, and part of a body covered with scales, from the Coal field near Leeds, are preserved in the museum of that town.

Sir Philip Grey Egerton has recently discovered scales of the Megalichthys, with teeth and bones of some other Fishes, and also Coprolites, in the Coal formation of Silverdale, and Newcastle-under-Line. These occur in a stratum of shale, containing shells of three species of Unio, with balls of argillaceous iron ore and plants.