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Magnesian limestone, forming about one-fifth of the total number yet observed in this formation. Very large bones of this voracious family occur in the lias of Whitby and Lyme Regis, and its genera abound throughout the Oolite formation. In the Cretaceous formations they become extremely rare.† They have not yet been discovered in any of the Tertiary strata; and in the waters of the present world are reduced to the two genera, Lepidosteus and Polypterus.

Thus we see that this family of Sauroids holds a very important place in the history of fossil Fishes. In the waters of the Transition period, the Sauroids and Sharks constituted the chief voracious forms, destined to fulfil the important office of checking excessive increase of the inferior families. In the secondary strata, this office was largely shared by Ichthyosauri and other marine Saurians, until the commencement of the Chalk. The cessation of these Reptiles and of the semi-reptile Sauroid Fishes in the Tertiary formations made room for the introduction of other predaceous families, approaching more nearly to those of the present creation.‡

*The Aspidorhynchus, from the Jurassic limestone of Solenhofen, (Pl. 27, Fig. 5,) represents the general character of the Sauroid Fishes.

+ The Macropoma is the only genus of Sauroid Fishes yet found in the Chalk of England.

Much light has been thrown on the history of Fishes in the Old red sandstone at the base of the Carboniferous series, by the discoveries of Professor Sedgwick and Mr. Murchison, in the bituminous schist of Caithness, (Geol. Trans. Lond. N. s. Vol. 3, part 1.;) and those of Dr. Traile, in the same schist in Orkney. Dr. Fleming also has made important observations on Fishes in the old red sandstone of Fifeshire. Farther discoveries have been made by Mr. Murchison of Fishes in the old red sandstone of Salop and Herefordshire. The general conditions of all these Fishes accord with those in the carboniferous series, but their specific details present most interesting peculiarities. Many of them will be figured by Mr. Murchison in his splendid Illustrations of the Geology of the Border Counties of England and Wales.

Fishes in Strata of the Carboniferous Order.

I select the genus Amblypterus (Pl. 27.,) as an example of Fishes whose duration was limited to the early periods of geological Formations; and which are marked by characters that cease after the deposition of the Magnesian lime

stone.

This genus occurs only in strata of the Carboniferous order, and presents four species at Saarbrück, in Lorraine ;* it is found also in Brazil. The character of the teeth in Amblypterus, and most of the genera of this early epoch, shows the habit of these Fishes to have been to feed on decayed sea-weed, and soft animal substances at the bottom of the water: they are all small and numerous, and set close together like a brush. The form of the body, being not calculated for rapid progression, accords with this habit.

The vertebral column continues into the upper lobe of the tail, which is much longer than the lower lobe, and is thus adapted to sustain the body in an inclined position, with the head and mouth nearest to the bottom.

Among existing cartilaginous Fishes, the vertebral column is prolonged into the upper lobe of the tail of Sturgeons and Sharks: the former of these perform the office of scavengers, to clear the water of impurities, and have no teeth, but feed by means of a soft leather-like mouth, capable of protrusion and

*The Fishes at Saarbück are usually found in balls of clay ironstone, which form nodules in strata of bituminous coal shale. Lord Greenock has recently discovered many interesting examples of this, and other genera of Fishes in the coal formation at Newhaven, and Wardie, near Leith. The shore at Newhaven is strewed with nodules of ironstone, washed out by the action of the tide, from shale beds of the coal formation. Many of these ironstones have for their nucleus a fossil Amblypterus, or some other Fish; and an infinitely greater number contain Coprolites, apparently derived from a voracious species of Pygopterus, that preyed upon the smaller Fishes.

contraction, on putrid vegetables and animal substances at the bottom; hence they have constant occasion to keep their bodies in the same inclined position as the extinct fossil Fishes, whose feeble brush-like teeth show that they also fed on soft substances in similar situations.*

The Sharks employ their tail in another peculiar manner, to turn their body in order to bring the mouth, which is placed downwards beneath the head, into contact with their prey. We find an important provision in every animal to give a position of ease and activity to the head during the operation of feeding.†

Fishes of the Magnesian Limestone, or Zechstein.

The Fishes of the Zechstein at Mansfeld and Eisleben have been long known, and are common in all collections; figures of many species are given by M. Agassiz. Examples of the Fishes of the Magnesian limestone of the north of England, are described and figured by Professor Sedgwick, in the Geol. Trans. of London, (2d Series, Vol. iii. p. 117, and Pl. 8, 9, 10.) He states in this paper (p. 99,) that the occurrence of certain Corals and Encrinites, and several species of Producta, Arca, Terebratula, Spirifier, &c. shows that the Magnesian limestone is more nearly allied in its

*At the siege of Silistria, the Sturgeons of the Danube were observed to feed voraciously on the putrid bodies of the Turks and Russian soldiers that were cast into that river.

† This remarkable elongation of the superior lobe of the tail is found in every bony Fish of strata anterior to and including the Magnesian limestone; but in strata above this limestone the tail is usually regular and symmetrical. In certain bony Fishes of the secondary period, the upper lobe of the tail is partly covered with scales, but without vertebræ. The bodies of all these Fishes also have an integument of rhomboidal body scales, covered with enamel.

No species of Fish has been found common to the Carboniferous group, and to the Zechstein or Magnesian limestone; but certain genera occur in both, e. g. the genus Palæoniscus and Polypterus.

zoological characters to the Carboniferous order, than to the calcareous formations which are superior to the New red sandstone. This conclusion accords with that which M. Agassiz has drawn from the character of its fossil Fishes.

Fishes of the Muschelkalk, Lias, and Oolite Formations.

The Fishes of the Muschelkalk are either peculiar to it, or similar to those of the Lias and Oolite. The figure engraved at Pl. 27, is selected as an example of the character of a family of Fishes most abundant in the Jurassic or Oolite formation; it represents the genus Microdon in the family of Pycnodonts, or thick-toothed Fishes, which prevailed extensively during the middle ages of Geological History. Of this extinct family there are five genera. Their leading character consists in a peculiar armature of all parts of the mouth with a pavement of thick round and flat teeth, the remains of which, under the name of Bufonites, occur most abundantly throughout the Oolite formation.* The use of this peculiar apparatus was to crush small shells, and small Crustacea, and to comminute putrescent seaweeds. The habits of the family of Pycnodonts appear to have been omnivorous, and their power of progression slow.†

Another family of these singular Fishes of the ancient world, which was exceedingly abundant in the Oolitic or Jurassic series, is that of the Lepidoids, a family still more

* Pl. 27c. Fig. 3. represents a five-fold series of these teeth on the palate of Pycnodus trigonus from Stonesfield; and Fig. 2, a series of similar teeth placed on the vomer in the palate of the Gyrodus Umbilicus from the great Oolite of Durrheim, in Baden.

A similar apparatus occurs in a living family of the Order Cycloids, in the case of the modern omnivorous Sea Wolf, Anarrhicas Lupus, and other recent Fishes of different families. M. Agassiz observes, that it is a common fact, in the class of Fishes, to find nearly all the modifications which the teeth of these animals present, recurring in several families, which in other respects are very different.

remarkable than the Pycnodonts for their large rhomboidal bony scales, of great thickness, and covered with beautiful enamel. The Dapedium of the lias (Pl. 1. Fig. 54.) affords an example of these scales, well known to geologists. They are usually furnished on their upper margin with a large process or hook, placed like the hook or peg near the upper margin of a tile; this hook fits into a depression on the lower margin of the scales placed next above it. (See Pl. 27, Figs. 3, 4, and Pl. 15, Fig. 17.) All Ganoidian Fishes, of every formation, prior to the Chalk, were enclosed in a similar cuirass, composed of bony scales, covered with enamel, and extending from the head to the rays of the tail. One or two species only, having this peculiar armature of enamelled bony scales, have yet been discovered in the Cretaceous series; and three or four species in the Tertiary formations. Among living Fishes, scales of this kind occur only in the two genera, Lepidosteus and Polypterus.

Not a single genus of all that are found in the Oolitic series exists at the present time. The most abundant Fishes of the Wealden formation belong to genera that prevailed through the Oolitic period.†

*The Pycnodonts, as well as the fossil Sauroids, have enamelled scales, but it is in the Leipidoids that scales of this kind are most highly developed. M. Agassiz has ascertained nearly 200 fossil species that had this kind of armour. The use of such a universal covering of thick bony and enamelled scales surrounding like a cuirass the entire bodies of so many species of Fishes, in all formations anterior to the Cretaceous deposites, may have been to defend their bodies against waters that were warmer, or subject to more sudden changes of temperature than could be endured by Fishes, whose skin was protected only by such thin, and often disconnected coverings, as the membranous and horny scales of most modern Fishes.

†The most remarkable of these are the genus Lepidotus, Pholidophorus, Pycnodus, and Hybodus.

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