266 
ORIGIN OF LIFE IN AMERICA 
during the Eocene Period the Greater Antilles were at -a 
higher level, so that the islands were united with one another 
and with Central America. This resulted in an exchange of 
species between the two regions. A land connection is also 
indicated between Cuba, the Bahamas and Florida. At this 
time, he thinks, the more northern isles of the Lesser Antilles 
were not yet elevated above the sea, or, if so, they have since 
probably been submerged. After this period of elevation 
there followed one of general subsidence. During it Jamaica 
was the first island to be separated, then followed Cuba, and 
afterwards Haiti and Portorico. The connection between 
the Antilles and the mainland was broken, while the subsi¬ 
dence continued until only the summits of the mountains of 
the four Greater Antillean Islands remained above water. 
Eventually there was another period of elevation which lasted, 
no doubt, until the present time. The Bahamas gradually 
emerged and were populated by forms drifted from Cuba and 
Haiti. In this last conclusion Dr. Simpson unfortunately 
fails to appreciate the full value of his own studies. If all 
the snails, amphibians and reptiles known to inhabit the 
Bahamas—and many of them are peculiar to these islands— 
had reached them by accidental dispersal, this mode of con¬ 
veyance must be of enormous importance. In such a case 
I think we should scarcely be justified in basing our theories 
of the geological history of the Antilles on the geographical 
distribution of animals. 
Now among the families of snails alluded to in Dr. Simp¬ 
son’s paper as being abundant in the West Indies, there are 
some that have received special attention by American 
malacologists. One of these, the Urocoptidae, or Cylindrel- 
lidae as they were formerly called, comprises small snails 
with an elegant fusiform shell composed of many narrow 
whorls. They are found in the Antilles, in southern Florida, 
along the northern coasts of South America, in Central 
America and in Mexico, as well as the adjacent parts of the 
United States. The centre of distribution thus lies in the 
West Indies. 
Since it has been proved by fossil evidence in Jamaica that 
numerous sub-generic groups of land snails, in essentially 
their modern forms, were established before the close of the 
