The Geographical Distribution of Fishes 253 



trout-like genus Galaxias, in New Zealand, South Australia, 

 and South America, that "there existed some terrestrial pas- 

 sage-way between the several regions at a time as late as the 

 close of the Mesozoic period. The evidence of such a connec- 

 tion afforded by congeneric fishes is fortified by analogous rep- 

 resentatives among insects, mollusca, and even amphibians. 

 The separation of the several areas must have occurred little 

 later than the late Tertiary, inasmuch as the salt-water fishes 

 of corresponding isotherms found along the coast of the now 

 widely separated lands are to such a large extent specifically 

 different. In general, change seems to have taken place more 

 rapidly among marine animals than fresh-water representatives 

 of the same class." 



In this case, when one guess is set against another, it seems 

 to me that the hypothesis first suggested, rather than the other, 

 lies in the line of least logical resistance. I think it better to 

 adopt provisionally some theory not involving the existence of 

 a South Pacific Antarctic Continent, to account for the dis- 

 tribution of Galaxias. For this view I may give five reasons: 



1. There are many other cases of the sort equally remark- 

 able and equally hard to explain. Among these is the presence 

 of species of paddle-fish and shovel-nosed sturgeon,* types char- 

 acteristic of the Mississippi Valley, in Central Asia. The pres- 

 ence of one and only one of the five or six American species of 

 pikef in Europe; of one of the three species of mud-minnow 

 in Austria, J the others being American. Still another curious 

 case of distribution is that of the large pike-like trout of the genus 

 Hticho, one species (Hucho hucho) inhabiting the Danube, the 

 other (Hucho blackistoni) the rivers of northern Japan. Many 

 such cases occur in different parts of the globe and at present 

 admit of no plausible explanation. 



2. The supposed continental extension should show per- 

 manent traces in greater similarity in the present fauna, both 

 of rivers and of sea. The other fresh- water genera of the re- 

 gions in question are different, and the marine fishes are more 



* The shovel-nosed sturgeon (Scaphirynchus and Kessleria) and the paddle- 

 fish (Polyodon and Psephurus). 

 f Esox lucius. 

 J Untrba, the mud-minnow. 



