Dlstrih„tl,,n of Fishes. 253 



8. Peculiar and common to .South America and Australia — 

 Perco|)liidid:o, llaplocliitonidio, Galaxiidic, and O.stco^los.sirUc. 



9. Peculiar and common to tropical and subtropical America 

 and Africa — Cichlidte, Characinida;, and Lcpidosirenida?. 



In addition to these, the family Cyprinidre is represented in 

 the entire cistropical or " arctoga2an " hemisphere as well as 

 in tropical Africa and Asia : and there are several monoty])ic 

 families limited to very small reunions, such .as the Comej)lio- 

 rid:v, the single species of which is only known from Lake 

 Baikal. There are, further, a number of families (in additi(jn 

 to several already mentioned) which are chiefly represented 

 by marine species, but which have also a greater or less 

 number of representatives in fresh water in different regions 

 of the earth ; such are the Brotulidie, Blenniidte, Gobiidoe, 

 Scia;nidcV, Atheriiiida^, ^lugilida?, Cyprinodontidic, ^Microsto- 

 midje, Clupeidje, Dorosomida^, &c. 



Others, again, Avere represented in former epochs in parts 

 of the world where they are not now found ; and especially to 

 be noted among these are two families at present characteristic 

 in their distribution : the first of these is the Cobitida?, which 

 in the early Tertiary were inhabitants of Western America, 

 and which thus increased the similarity of the fauna of our 

 (cistropical) continent to that of Northern Asia ; the second 

 is the Ceratodontida?, a family whose representatives have 

 long been known from fossil teeth found in Palfeozoic and 

 Mesozoic deposits (and which were referred by Prof. Agassiz 

 to the sharks), and had been supposed to have expired towards 

 the end of the Triassic epoch ; yet recently (since 1870) two 

 species, closely allied to those found in the Triassic beds of 

 Europe, have been discovered living in Australia ; and thus 

 another ancient type has been preserved in that continent to 

 illustrate the past life of our own hemisphere. 



If we now seek to apply the knowledge thus gained to the 

 appreciation of the origin of the different fish-faunas of the 

 globe, we are forced to the following conclusions. 



Inasmuch as the cistropical hemisphere shares in common 

 the same families, and to a considerable extent the same 

 genera (and even some species), it is presumable that the dif- 

 ferent regions of that hemisphere have derived their inhabitants 

 from a common primitive source, although North America has 

 quite a large proportion of forms peculiar to it. The relation 

 of these peculiar forms, however, are in all cases rather with 

 some found in the northern hemisphere (freshwater or marine) 

 than with any found elsewhere ; but, at the same time, towards 

 the south-western limits of the United States occur repre- 

 sentatives of families which are characteristic of tropical 



Avn. cC- J%. a: Tfist. Ser. 4. !>./. xv. 18 



