238 STALK-EYED CRUSTACEA. 
dian genera but also of species closely allied to those of the West Indies, 
point to a common origin of these two faun in the great Caribbaeo-Mexican 
Gulf which formerly opened freely into the Pacific over the region now 
occupied by Central America and Mexico.* This communication between 
the Caribbean Sea and the Pacific was not barred at the Isthmus of Darien 
apparently before the Miocene.t 
The relationship between the littoral faunze of the Atlantic and Pacific 
coasts of tropical America has often been pointed out by writers on the dif- 
ferent classes of marine animals. Even before geological evidence was avail- 
able a former water-way across the Isthmus of Darien was invoked to explain 
the existence of identical or analogous species on the opposite shores. 
In 1856 Philip P. Carpenter + made a comparison between the littoral 
Mollusca of the Atlantic and Pacific shores of tropical America, and listed as 
common to both shores 35 identical species, and 54 species likely to prove 
identical ; together with 67 Pacific species represented in the West Indies by 
closely allied or analogous species. He also pointed out the general dissimi- 
larity of the Panamian and Indo-Pacific Molluscan faunee. On comparing the 
marine Mollusca of Panama with those of the West Indies, Mérch§ con- 
cluded that the Panama Province, although geographically a part of the 
Pacific, yet faunally belonged to the tropical Atlantic, its affinities with the 
Indo-Pacific region being comparatively remote. 
Later conchologists, by nicer discrimination, have very much reduced the 
number of identical species, but have not thereby effaced the relationship 
between the two faune. Even Fischer, 
| who believes that the affinity 
between the faunz of the opposite sides of the Isthmus is much more 
remote than has been maintained by many writers, admits the striking 
distinctness of the Panama fauna from the Indo-Pacific. 
Of the 195 kinds of Central American shore Fishes known to Dr. Giinther** 
in 1869, 59 (or 50} p. ec.) were found on both the east and west coasts. Ina 
later work ++ the same author asserts that the genera of Fishes are with 
* See A. Agassiz, Mem. Mus. Comp. Zodl., X., No. 1, p. 82, 1883; Bull. Mus. Comp. Zoél., XIV. 112, 
1888. 
t See W. M. Gabb, Proc. Amer. Philosoph. Soc., XII. 571, 572, 1872, and Dall and Harris, Bull. U.S. 
Geolog. Surv., No. 84, p. 151, 1892. 
t Rep. Brit. Assoc. Adv. Sci. for 1856, pp. 362 ef seqg., 1857. 
§ Beitrage zur Molluskenfauna Central-Amerika’s, von O, A. L. Mérch. Malakozoolog. Blatter, 
herausgeg. v. Menke u. Pfeiffer, VI. 107, 1860. 
| Manuel de Conchyliologie, p. 167, 1881. 
** Trans. Zodlog. Soc. London, VI. 397, 1869. 
tt Introduction to the Study of Fishes, pp. 279, 280, 1880. 
