It is almost superfluous to remark that hardly any fossil-fish are known from south of the equator; and by running through Pictet's Palaeontology it will be seen that very few species are known from several formations in Europe.

Some few families of fish now have a confined range; the teleostean fishes might formerly have had a similarly confined range, and after having been largely developed in some one sea, have spread widely.

Nor have we any right to suppose that the seas of the world have always been so freely open from south to north as they are at present.