PROGRESS IN BIOLOGICAL INQUIRIES, 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 
