NO. 16 MANTER: DISTRIBUTION OF DIGENETICTREMATODES 543 



interest to group the trematodes of the mainland in the same manner 

 as has been done above for Galapagos trematodes. Twenty-one species 

 were collected; 9 species were endemic; 12 species were fovmd or are 

 known elsewhere. The nearest related species of the endemic trematodes 

 indicate no single similar region. Two of such related species are from 

 Japan, one from Panama; one from Australia; one from Europe; one 

 from North Carolina and Tortugas; none from the Galapagos. Of the 

 12 nonendemic species, 6 occur along the Pacific coast of Mexico or 

 Panama (all 6 are known only from there) ; 4 occur at Tortugas (one of 

 these only from there) ; 3 occur at Galapagos (one of these only from 

 there) ; 2 occur in Japan (one of these only from there). Therefore, the 

 nonendemic species from the Pacific coast of South America show most 

 relationship to the Pacific coast of Mexico and some slight similarity to 

 the fauna of Tortugas, Galapagos Islands, and Japan. 



DISCUSSION 



The foregoing material reveals a very pronounced similarity between 

 the trematode fauna of the tropical American Pacific and the tropical 

 American Atlantic. In fact, the similarity is almost as great as would be 

 expected if the two oceans were still continuous. Judging from the trema- 

 tode faunas, the Galapagos Islands might seem almost to be a part of the 

 West Indian archipelago. The regions of the world most similar to the 

 Galapagos Islands, judging from the trematodes collected, are in order: 

 (1) the region of Tortugas, Florida; (2) the west coast of Mexico; (3) 

 Japan; (4) northern Pacific coast of America; (5) Pacific coast of South 

 America. However, it should be noted that the Tortugas region in com- 

 parison with the Galapagos region has a somewhat dififerent status than 

 the Pacific coastal waters in that many more fishes from the Florida 

 waters have been examined. Probably more examinations along the Mexi- 

 can coast would reveal additional Galapagos species there. Such findings 

 would not alter the similarity between the Galapagos and Tortugas 

 faunas, and the general tendencies indicated in the above tables would 

 remain more or less marked. If, when the Pacific Mexican fauna is as 

 well known as the Tortugas fauna, it should be found that the Galapagos 

 region was still more similar to Tortugas than to Mexico, the evidence 

 would indicate considerable age for the Galapagos Islands. 



Other kinds of evidence indicate that Galapagos affinities are strongly 

 Atlantic in nature. A submarine plateau of relatively shallow water (less 



