AFFINITIES OF TWO OCEANS 333 



floor may, I think, be explained in an entirely different way. 

 We might possibly expect a condition such as Mr. Agassiz 

 describes off the mouths of the Amazon or Orinoco rivers, but 

 there are no vast rivers anywhere on the Pacific coast to fur- 

 nish all this vegetable detritus he speaks of. A similar condi- 

 tion, moreover, occurs only to a very limited extent on the 

 Atlantic side of the isthmus. That the ocean floor is covered 

 with tree trunks, twigs and other vegetable detritus may be 

 due to the existence within recent geological times of a well- 

 timbered land between Central America and the Galapagos 

 islands which has since vanished beneath the ocean. 



And yet that all was not land on the Pacific side of Central 

 America is proved by many distinct lines of evidence. 



Mr. Guppy * tells us that Laguncularia racemosa, Rhizo- 

 phora mangle, Anona paludosa and ConO'carpus erectus, all 

 of which are plants of the mangrove formation, occur not 

 only on the Pacific and Atlantic coasts of America, but also 

 on the west coast of Africa. We cannot suppose that such 

 characteristic sea -shore species can be conveyed across a land 

 area by any known means of accidental dispersal. Moreover, 

 since that vegetation does not occur south of the Bay of Guaya- 

 quil, it could not have reached the coast of Ecuador from 

 eastern South America by travelling round Cape Horn. Thus 

 the most likely explanation of the occurrence of the flora on 

 both sides of Central America is to assume the existence of 

 a former continuous shore line between Ecuador and Vene- 

 zuela. 



In the list of stalk-eyed Crustacea found on the coast of 

 Peru, Miss Eathbun f reports that a few species of crabs, like 

 Acanthonyx petiverii, Microphrys platysoma, Panopeus ber- 

 mudensis and Geograpsus lividus, are common to both sides 

 of Central America, while a most striking feature is the 

 faunistic uniformity of the marine area between the Cape 

 Eegion of Lower California and the coast of Chile. Dr. 

 DallJ divided this whole fauna into two provinces, viz., the 

 Panamic, extending from Lower California to Guayaquil, and 

 the Peruvian, from the latter to the island of Chiloe in Chile, 



* Guppy, H. B., "A Naturalist in the Pacific," p. 498. 

 t Eathbun, M. J., " Stalk-eyed Crustacea of Peru." 

 | Ball, W. H., " Eeport on the Shells of Peru," p. 185. 



