238 STALK-EYED CRUSTACEA. 



dian ■"■enerii but also of species closely allied to those of the West Indies, 

 point to a common origin of these two faunai in the great Caribbseo-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.! 



The relationship between the littoral faunae of the Atlantic and Pacific 

 coasts of tropical America has often been pointed out by writers on the dif- 

 ferent classes of m.nrine 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 compai'ison between the littoral 

 Mollusca of the Atlantic and Pacific shores of tropical America, and listed as 

 common to both shores 35 identical species, artd 34 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 faunte. On comparing the 

 marine Mollusca of Panama with those of the West Indies, Morch § 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 faunae. Even rischer,|| who believes that the affinity 

 between the faunjB 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 193 kinds of Central American shore Fishes known to Dr. Giinther** 

 in 1869, 59 (or 30| p. c.) were found on both the cast and west coasts. In a 

 later work ft the same author asserts that the genera of Fishes are with 



• See A. Agassiz, Mem. Mus. Comp. Zool , X., No. 1, p. 82, 18S3 ; Bull. Mus. Conip. Zo6l., XIV. 112, 

 1S88. 



t Sec W. M. Gabb, Proc. Amer. Pliilosopli. Soc, XII. 571, 572, 1872, and Dall and Harris, Bull. U. S. 

 Geolog. Surv., No. 84, p. 151, 1892. 



X Rep. Brit. Assoc. Adv. Sci. for 1856, pp. 362 et seqq., 1857. 



§ Bcilrage zur MoUuskenfauna Ccnfral-Amerika's, vou 0. A. L. Morch. Iilalakozoolog. Blatter, 

 hcrausfjc^. y. Menke u. PfcifTer, VL 107, 18G0. 



II Maimcl dc Conchyliologie, p. 167, 1881. 



•• Trans. Zoolog. Soc. London, VI. 397, 1869. 



tt Introduelion to the Study of Fishes, pp. 279, 280, 1880. 



