268 
ORIGIN OF LIFE IN AMERICA 
this old land was submerged having since gradually regained 
its present position. 
The great age of the West Indian fauna and the inter-re¬ 
lationship between the islands and the mainland is well exem¬ 
plified by the ancient family of operculate snails—the 
Cyclophoridae.* The genus Neocyclotus inhabits principally 
northern South America and the Antilles. From this 
apparently very old centre of dispersal some members of 
the genus have pushed southward as far as Peru in the west 
and Rio de Janeiro in the east. A few have entered Central 
America. One distinct group (Plectocyclotus) has no less 
than thirty-two species in Jamaica and only one in Portorico. 
Another genus (Crocidopomai) is entirely confined to Jamaica, 
Haiti and eastern Cuba. This indicates strikingly the re¬ 
lationship of the three Great Antilles and their distinctness 
from western Cuba, which was already pointed out by Dr. 
Pilsbry, while geologists maintain that western Cuba was 
submerged quite independently from the remainder of the 
islands. It also illustrates the extreme slowness with which 
the dispersal of these mollusks takes place. 
Still more instructive is the whole group to which 
C'rocidopoma belongs. With Cyrtotoma, Amphicyclotus and 
Buckleya, it forms, as already mentioned (p. 256), a group 
of closely related genera of operculate snails. I alluded 
also to the fact that three of them had a discontinuous range 
in Central America, and that Amphicyclotus had apparently 
travelled eastward from Ecuador, invading Venezuela and 
Guiana, and had thence passed into the islands of Martinique, 
Guadeloupe and Dominica, when the latter were connected 
with one another, and with the mainland. It might be 
urged that accidental dispersal is responsible for their 
presence on these islands. 'But we have no reason for such a 
supposition, because the species occurring on the islands are 
quite distinct from one another and from those of Venezuela. 
Some evidence is afforded by these snails for the belief that 
the Lesser Antilles are remnants of older land which ex¬ 
tended northward from Venezuela, although all the visible 
parts of the islands are covered by modern volcanic deposits. 
* Ivobelt, W., “ Cyclophoridae.” 
