DK. GtTNTHEK ON THE FISHES OF CENTRAL AMEEICA. 397 



Pristis, Lath. 



301. antiquoruni, Lath Atl. &; Pac. Oceans (Chiapam) ^I- 



Urolophus, Milll. &|- Henle. 



302. *mundus, Gill Pac ^^■ 



Aetobatis, MiiU. i>; Henle. 



303. *latirostris, A. Bum Gaboon, Panama ^I- 



§ 6. Partial Idmtity of the Fish-faunas of the Atlantic and Pacific Coasts of 



Central America. 



It will be seen that, as far as our present knowledge reaches, of these 303 species, 

 173 are truly marine forms, 57 being found on both sides of the Isthmus. 

 25 have been found in brackish water, of which 3 are found on both sides of the 



Isthmus. 

 101 are freshwater fishes, 17 being found in rivers of the Atlantic and Pacific sides. 

 There will be but very few species which are entirely limited to brackish water, and 

 which may not be with equal propriety added either to the marine or freshwater fauna. 

 Thus, five of the 25 species hitherto known from lagoons with brackish water belong 

 to freshwater genera ; and, admitting two groups only, we have 



193 marine fish, 59 of which are found on both sides of Central America=30i 



per cent. 

 106 freshwater fish, 19 being found in rivers of the Atlantic and Pacific sides = 18 



per cent. 

 From the circumstance that our collectors paid more attention to the freshwater 

 than to the marine fauna (at least of the Atlantic coast), we may assume that the pro- 

 portion between the two groups will be increased by future researches in favour of the 

 marine fauna, but that the proportion between species peculiar to one side and those 

 common to both will be lessened, inasmuch as every collector will discover other 

 Atlantic forms on the Pacific side, and vice versd. 



The very curious fact of the partial identity of the species of both coasts of Central 

 America was first distinctly stated by myself in the Society's ' Proceedings ' for 1861 

 (p. 370), when, out of fourteen species collected by Capt. Dow on the Pacific side, five 

 were found to be Atlantic forms. To these vai-ious others were added by me in the 

 ' Catalogue of Fishes ; ' and Mr. Gill confirmed this observation in Proc. Ac. Nat. Sc. 

 Philad. 1862, pp. 140, 249. Professor Wagner, in his memoir quoted above (p. 384)', 

 has made the same observation ; but the species enumerated by him, fourteen in number, 

 are, with one exception, freshwater forms, the geographical distribution of which must 

 have been brought about at periods and in ways different from those of the diffusion 

 of marine species. 



Knowing now that at least 30 per cent, of the marine fish are found on both sides of 

 ' See also ' llecord, Zool. Literal." ii. p. 177. 



