REPTILIA, BATRACHIA, AND PISCES. 
By C. Tate Reaan, M.A. 
It has been found convenient to deal with these groups in the reverse order to that 
indicated in the heading of the chapter, and to take the Fishes first. 
PISCES. 
Marine Fishes.—It is well known that the fishes of the Pacific coast of America, 
from California to Peru, are quite distinct from those of the tropical Indo-Pacific, and 
are related to those of the Antillean district. At one time it was thought that a large 
proportion of the species were found on both the Atlantic and Pacific coasts, but the 
most recent work tends to show that when pelagic fishes of wide distribution are 
eliminated the number of species identical on the two coasts is very small. ‘There 
are, however, many closely related species that represent each other on the Atlantic 
and Pacific coasts, and the inference is that each pair has evolved from a parent form 
that existed when the two oceans were connected, ‘There is evidence that North and 
South America were separated by sea during the Eocene, and became one continent 
in the Miocene; if this were so, the similarity and degree of dissimilarity between 
the tropical shore-fishes of the Atlantic and Pacific coasts would be satisfactorily 
explained. 
Fresh-water Fishes.—Fishes that are found in lakes and rivers sometimes belong 
to marine species that enter fresh water for purposes of breeding or feeding; such 
species may form permanent fresh-water colonies or races, and these lead to fresh-water 
species of marine genera and fresh-water genera of marine families. These are 
unimportant in zoo-geography, but there are many families and even some orders that 
are confined to fresh water, and appear to have evolved their genera and species iu 
fresh water; their dispersal has depended on hydrographical changes, such as the unioa 
of rivers formerly distinct or the capture by one stream of the tributaries of another, 
and for most of them the sea appears to be an impassable barrier. Such fishes may be 
termed true fresh-water fishes, and they are of the highest importance as indicating 
former land-connectious or ancient lines of severance. 
The Neotropical Region.—South America has a rich and varied fish-fauna, 
surpassing that of any other region for wealth and individuality. As in other parts 
of the world, except the Australian Region, the majority of the true fresh-water fishes 
belong to the order Ostariophysi*. This order comprises.two well-marked suborders, 
* Of, Ann. & Mag. Nat, Hist. (8) viii. 1911, pp. 13-32, 553-577. 
BIOL. CENTR.-AMER., Introd. Vol., June 1915. P 
