OF SAUROID FISHES. 
277 
have not yet been discovered in any of the 
Tertiary strata; and in the waters of the pre- 
sent world are reduced to the two genera, Le- 
pidosteus 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 Ichthyo- 
sauri and other marine Saurians, until the com- 
mencement 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, ap- 
proaching more nearly to those of the present 
creation.* 
* 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 ].); and those of Dr. Trade, in the same schist in Orkney, 
b^r. 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 sand.stone 
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. 
