272 Isthmus Barriers Separating Fish Faunas 



In 1869 Dr. Gunther, after enumerating the species exam- 

 ined by him from Panama, reaches the conclusion that nearly 

 one-third of the marine fishes on the two shores of tropical 

 America will be found to be identical. He enumerates 193 such 

 species as found on the two coasts; 59 of these, or 31 per cent, 

 of the total, being actually identical. From this he infers that 

 there must have been, at a comparatively recent date, a de- 

 pression of the Isthmus and intermingling of the two faunas.* 



Catalogue of Fishes of Panama. In an enumeration of the 

 fishes of the Pacific coast in 1885,! the present writer showed 

 that Dr. Gunther's conclusions were based on inadequate data. 



In my list 407 species were recorded from the Pacific coast 

 of tropical America twice the number enumerated by Dr. 

 Gunther. Of these 71 species, or 17^ per cent., were found 

 also in the Atlantic. About 800 species are known from the 

 Caribbean and adjacent shores, so that out of the total number 

 of 1,136 species but 71, or 6 per cent, of the whole, are common 

 to the two coasts. This number does not greatly exceed that of 

 the species common to the West Indies and the Mediterranean, 

 or even the West Indies and Japan. It is to be noted also 

 that the number 71 is not very definitely ascertained, as there 

 must be considerable difference of opinion as to 'the boundaries 

 of species, and the actual identity in several cases is open to 

 doubt. 



This discrepancy arises from the comparatively limited rep- 

 resentation of the two faunas at the disposal of Dr. Gunther. 

 He enumerates 193 marine or brackish-water species as found 

 on the two coasts, 59 of which are regarded by him as specific- 

 ally identical, this being 31 per cent, of the whole. But in 

 30 of these 59 cases I regard the assumption of complete identity 

 as erroneous, so that taking the number 193 as given I would 

 reduce the percentage to 15. But these 193 species form but 

 a fragment of the total fauna, and any conclusion based on 

 such narrow data is certain to be misleading. 



Of the 71 identical species admitted in our list, several (e.g., 

 Mola, Thunnus) are pelagic fishes common to most warm seas. 



* "Fishes of Central America," 1869, 397. 

 \Proc. U. S. Nat. Mus., 1885, 393. 



