Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/215

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.^[1] In the Cretaceous formations they become extremely rare.^[2] 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.^[3]

1. The Aspidorhynchus, from the Jurassic limestone of Solenhofen, (Pl. 27a, Fig. 5,) represents the general character of the Sauroid Fishes.
2. The Macropoma is the only genus of Sauroid Fishes yet found in the Chalk of England.
3. 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. Further 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.