AFFINITIES OF TWO OCEANS 
383 
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 Conocarpus 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 Rathbun 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 
Region of Lower California and the coast of Chile. Hr. 
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 Rathbun, M. J., “ Stalk-eyed Crustacea of Peru.” 
t Dali, W. H., “Report on the Shells of Peru,” p. 185. 
