PKOGEJESS m BIOLOGICAL INQUIEIES, 1921. 



15 



FISHES OF THE PANAMA REGION. 



The Bureau of Fisheries, late in 1910, entered into an agreement 

 with the Smithsonian Institution and the Field Museum of Natural 

 History for a cooperative study of the fishes of the Panama Canal 

 Zone. The work was carried on under the auspices of the Smith- 

 sonian Biological Survey of the Panama Canal Zone. The field work 

 was done by Dr. Seth E. Meek, of the Field Museum, and Samuel F. 

 Hildebrand, of the Bureau of Fisheries, during two expeditions made 

 to the Canal Zone, from January to June, 1911, and January to 

 March, 1912, respectively. The study of the collections which were 

 sent to the National Museum was begun during the interval between 

 the two expeditions and continued after the second visit to Panama 

 by the collectors. After two small preliminary papers containing 

 descriptions of new species of fresh-water fishes had been written, 

 and a majority of the forms had been roughly identified and sepa- 

 rated, Dr. Meek was obliged to withdraw from the work because of 

 an illness from which he never recovered. The completion of the work 

 was then left to Mr. Hildebrand. As other duties were necessarily 

 assigned to Mr. Hildebrand from time to time, the completion of the 

 study of the collections was greatly delayed. The final report on the 

 fresh-water fishes, however, was completed and published in 1916, but 

 the study of the marine forms was not completed until the spring of 

 1921. In the last months of the work the author was assisted by 

 W. C. Schroeder. 



The total number of species recorded from the coasts of Panama, 

 either taken by Messrs. Meek and Hildebrand, or previous collectors, 

 or both, is 640. The remainder of the species included in the paper 

 were discussed because their known range of distribution is such 

 that they may be expected on the coasts of the Isthmus. The fishes 

 on the Pacific coast run larger than those on the Atlantic and are 

 more numerous both as to species and individuals. Much more col- 

 lecting, however, has been done on the Pacific side than on the At- 

 lantic, which undoubtedly accounts in part for the large difference 

 in the number of species recorded. The total number of species listed 

 as common to both coasts of Panama is 72, but of these 48 are more 

 or less cosmopolitan in their distribution, that is, they are not con- 

 fined to American waters. A very large number of species consid- 

 ered distinct are, however, very closely related, differing only slightly 

 but in apparently constant characters. 



It was pointed out in the report on the fresh-water species that the 

 fishes of the opposite slopes of Panama are very closely related, some 

 of them remaining identical. This close relationship indicates that 

 the fishes of the two slopes had not long been separated. Since the 

 opening of the Canal they, of course, can again freely intermingle 

 in those streams which are connected with the Canal. The close 

 parallelism of the marine species of the opposite coasts is evidence 

 of a comparatively recent passageway from ocean to ocean, even for 

 salt-water forms. The genera of many families have representatives 

 on both coasts, and if they do not include identical species they at 

 least have very closely related forms on the opposite coasts. A few 

 families, however, deviate from this general rule in having many 

 more representatives on one coast than on the other. The reasons 



