October 11, 1901.] 



SCIENCE, 



555 



most cases they are appreciable, especially 

 in fresh specimens. 



Further, I expressed the belief that 

 " fuller investigation will not increase the 

 proportion of common species. If it does 

 not, the two faunas show no greater resem- 

 blance than the similai'ity of physical con- 

 ditions on the two sides would lead us to 

 expect." 



This conclusion must hold so far as spe- 

 cies are concerned, but the resemblance in 

 the list of genera is too great to be ac- 

 counted for in this way. 



OBSERVATIONS OF DR. GUNTHER. 



In 1880 * Dr. Giinther expressed his views 

 in still stronger language, claiming a still 

 larger proportion of the fishes of tropical 

 America to be identical on the two sides of 

 the continent. He concluded that "with 

 scarcely any exceptions the genera are 

 identical, and of the species found on the 

 Pacific side, nearly one half have proved to 

 be the same as those of the Atlantic. The 

 explanation of this fact has been found in 

 the existence of communications between 

 the two oceans by channels and straits 

 which must have been open till within a 

 recent period. The isthmus of Central 

 America was then partially submerged, and 

 appeared as a chain of islands similar to 

 that of the Antilles ; but as the reef- build- 

 ing corals flourished chiefly north and east 

 of these islands and were absent south and 

 west of them, reef fishes were excluded 

 from the Pacific shores when the communi- 

 cations were destroyed by the upheaval of 

 land." 



CONCLUSIONS OF EVERMANN AND JENKINS. 



This remark led to a further discussion 

 of the subject on the part of Dr. B. W. Ever- 

 mann and Dr. O. P. Jenkins. From their 

 paper on the fishes of Guaymasf I make 

 the following quotations : 



* ' Introduction to the Study of Fishes, ' 1880, p. 280. 



tProc. U. S. Nat. Mus., 1891, pp. 124-126. 



" The explorations since 1885 have re- 

 sulted, (1) in an addition of about one 

 hundred species to one or other of the two 

 faunfB ; (2) in showing that at least two 

 species that were regarded as identical on 

 the two shores * are probably distinct ; and 

 (3) in the addition of but two species to 

 those common to both coasts, y 



" All this reduces still further the per- 

 centage of common species. 



"Of the one hundred and ten species ob- 

 tained 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 hypoth- 

 esis of a former waterway through the isth- 

 mus to account for their presence on both 

 sides. They are species fully able to ar- 

 rive 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 hy- 

 pothesis 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 difierent from 

 the figures given by Dr. Giinther 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 com- 

 mon to the two coasts that bear very 

 closely upon the waterway hypothesis. 

 This is less than 4-3 per cent, of the ivhole num- 

 ber.'' 



" But the evidence obtained from a study 



* CUharicMhys spilopterus »nd C. gilberti. 



-f Hxmulonsieindachneri and Gymnothorax casianeus 

 of the west coast probably being identical with H. 

 schranki and Gymnothorax funcbris of the east coast. 



