238 



STALK-EYED CRUSTACEA. 



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dian genera but also of species closely allied to those of the West Indies, 

 point to a common origin of these two fauna) in the great Caribba30-Mexicaii 

 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 Isthnius of Darien 



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apparently before the Miocene. t 



The relationship between the littoral fauna) of the Atlantic and Pacific 

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



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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 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 fauna3. On comparing the 

 marine Mollusca of Panama with those of the West Indies, Morch§ con- 

 cluded that the Panama Pi^ovince, although geographically a part of the 



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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 tden&al species, but have not thereby effaced the relationship 

 between the two fauna). Even Fischer,|| who believes that the affinity 

 between the fauna) 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** 



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in 1869, 59 (or 30|- p. c.) were found on both the east and w^est 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, 1883 ; Bull Mas. Comp. ZooL, XIV. 112, 

 1888. 



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

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



J Hep. Brit. Assoc. Adv. Sci. for 1856, pp. 362 et seqq., 1857. 



§ Beitrage zur Molliiskcnfauna Ccntral-Amerika's, von 0. A. L. Morcli. Malakozoolog. Blatter, 

 herausgeg. v. Menke u. Pfeiffer, VI. 107, 18G0. 



II Manuel de Conclijllologie, p. 1G7, 1881. 



** Trans. Zoolog. Soc. London, VL 307, 1869. 



tt Introduction to the Study of Pishes, pp. 279, 280, 1880. 



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