The geographical distribution of animals, with a study of the relations ...

1GG DISTRIBUTION OF EXTINCT ANIMALS. [part ii.is allied to the Menopoma living in North America. Speciesof frog (Bana), and Palceophryus an extinct genus of toads,have been found in the Miocene deposits of Germany andSwitzerland.Fresh water fish are almost unknown in the Tertiarydeposits of Europe, although most of the families and somegenera of living marine fish are represented from the Eocenedownwards.Antiquity of the Geneka of Insects.Fossil insects are far too rarely found, to aid us in our determinationof difficult questions of geographical distribution ; but indiscussing these questions it will be important to know, whetherwe are to look upon the existing generic forms of insects as ofgieat or small antiquity, compared with the higher vertebrates ;and to decide this question the materials at our command areample.The conditions requisite for the preservation of insects in afossil state are no doubt very local and peculiar ;the result being,that it is only at long intervals in the geological record that wemeet with remains of insects in a recognisable condition. Noneappear to have been found in the Pliocene formation ; but in theUpper Miocene of (Eninghen in Switzerland, associated with thewonderfully rich fossil flora, are found immense quantities ofinsects. Prof. Heer examined more than 5,000 specimens belongingto over 800 species, and many have been found in otherlocalities in Switzerland ;so that more than 1,300 species ofMiocene insects have now been determined.Most of the ordersare represented, but the beetles (Coleoptera) are far the mostabundant.Almost all belong to existing genera, and the majorityof these genera now inhabit Europe, only three or four beingexclusively Indian, African, or American.In the Lower Miocene of Croatia there is another rich depositof insects, somewhat more tropical in character, comprisinglarge white-ants and dragon-flies differently marked from any