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 email 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 tJie 

 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 



