274 Isthmus Barriers Separating Fish Faunas 



Conclusions of Evermann and Jenkins. This remark led to 

 a further discussion of the subject on the part of Dr. B. W. 

 Evermann and Dr. O. P. Jenkins. From their paper on the 

 fishes of Guaymas* I make the following quotations: 



"The explorations since 1885 have resulted (i) in an addi- 

 tion of about 100 species to one or other of the two faunas; 

 (2) in showing that at least two species that were regarded as 

 identical on the two shores t are probably distinct; and (3) in 

 the addition of but two species to those common to both coasts, t 



"All this reduces still further the percentage of common 

 species. 



"Of the no species obtained by us, 24, or less than 21 

 per cent., appear to be common to both coasts. Of these 24 

 species, at least 16, from their wide distribution, would need 

 no hypothesis of a former waterway through the Isthmus to 

 account for their presence on both sides. They are species 

 fully able to arrive at the Pacific shores of the Americas 

 from the warm seas west. It thus appears that not more than 

 eight species, less than 8 per cent, of our collection, all of which 

 are marine species, require any such hypothesis to account for 

 their occurrence on both coasts of America. This gives us, 

 then, 1,307 species that should properly be taken into account 

 when considering this question, not more than 72 of which, or 

 5.5 per cent., seem to be identical on the two coasts. This is 

 very different from the figures given by Dr. Gunther in his 

 'Study of Fishes.' 



"Now, if from these 72 species, admitted to be common to 

 both coasts, we subtract the 16 species of wide distribution 

 so wide as to keep them from being a factor in this problem - 

 we have left but 56 species common to the two coasts that bear 

 very closely upon the waterway hypothesis. This is less than 

 4.3 per cent, of the whole number. 



"But the evidence obtained from a study of other marine 

 life of that region points to the same conclusion. 



* Proc. U. S. Nat. Mus., 1891, pp. 124-126. 



t Citharichthys spilopterus and C. gilberti. 



% Hcemulon steindachneri and Gymnothorax castaneus of the west coast 

 probably being identical with H. schranki and Gymnothorax funebris of the 

 east coast. 



