genera, species, and individuals; the forms are exclusively marine, and the remains in the most perfect condition. * * * * * In the _Tertiary_ epoch the Teleosteans have almost entirely replaced the Ganoids; a few species only of the latter make their appearance, and they belong to existing genera, or, at least, very closely allied forms (_Lepidosteus_, _Amia_, _Hypamia_, _Acipenser_). The Chondropterygians merge more and more into recent forms; Holocephali continue, and still are better represented than in the present fauna. The Teleosteans show even in the Eocene a large proportion of existing genera, and the fauna of some localities of the Miocene (Oeningen) is almost wholly composed of them. On the whole, hitherto more than one-half have been found to belong to existing genera, and there is no doubt that the number of seemingly distinct extinct genera will be lessened as the fossils will be examined with a better knowledge of the living forms. The distribution of the fishes differed widely from that of our period, many of our tropical genera occurring in localities which are now included within our temperate zone, and being mixed with others, which nowadays are restricted to a colder climate: a mixture which continues throughout the Pliocene. * * * * * A few families of fishes, like the freshwater Salmonidæ, seem to have put in their appearance in _Post-pliocene_ times; however, not much attention has been paid to fish-remains of these deposits; and such as have been incidentally examined offer evidence of the fact that the distribution of fishes has not undergone any further essential change down to the present period. [See _E. Sauvage_, Mémoire sur la Faune Ichthyologique de la période Tertiaire. Paris 1873. 8°.] [Illustration: Fig. 102.--_Pycnodus rhombus_, a Ganoid from the Upper Oolite.] CHAPTER XVI. THE DISTRIBUTION OF EXISTING FISHES OVER THE EARTH’S SURFACE--GENERAL REMARKS.