Cyprinoids, belonging to genera living as well as extinct, existed in North America in the tertiary period. At present, _Cyprinina_, _Leuciscina_, and _Abramidina_ are well represented, but there is no representative of the Old World genus _Barbus_, or of the _Cobitidina_[26]; _Rhodeina_ are also absent. On the other hand, a well-marked Cyprinoid type is developed--the _Catostomina_, of which one species has, as it were, returned into Asia. Very characteristic is the group of _Centrarchina_, allied to the Perch, of which there are some thirty species; two _Grystina_. Of the Sticklebacks there are as many species as in Europe, and of Pike not less than seven species have been distinguished. _Umbra_ appears to be as local as in Europe. Some very remarkable forms, types of distinct families, though represented by one or two species only, complete the number of North American autochthont fishes--viz., _Aphredoderus_, _Percopsis_, _Hyodon_, and the _Heteropygii_ (_Amblyopsis_ and _Chologaster_). The last are allied to the Cyprinodonts, differing from them in some points of the structure of their intestines. The two genera are extremely similar, but _Chologaster_, which is found in ditches of the rice-fields of South Carolina, is provided with eyes, and lacks the ventral fins. _Amblyopsis_ is the celebrated Blind Fish of the Mammoth Cave of Kentucky: colourless, eyeless, with rudimentary ventral fins, which may be occasionally entirely absent. A peculiar feature of the North American Fish Fauna is that it has retained, besides the Sturgeons and Lampreys, representatives of two Ganoid families, _Lepidosteus_ and _Amia_. Both these genera existed in tertiary times: the former occurs in tertiary deposits of Europe as well as North America, whilst fossil remains of _Amia_ have been found in the Western Hemisphere only. It is difficult to account for the presence of the _Amiurina_ in North America. They form a well-marked division of the _Bagrina_, which are well represented in Africa and the East Indies, but absent in South America; it is evident, therefore, they should not be regarded as immigrants from the south, as is the case with the Palæarctic Siluroids. Nor, again, has the connection between South and North America been established sufficiently long to admit of the supposition that these Siluroids could have spread in the interval from the south to the northern parts of the continent, for some of the species are found as far north as Pine Islands Lake (54° lat. N.)[27] III. SOUTHERN ZONE.