176 ORIGIN OF LIFE IN AMERICA 



Period by a land passage, but does not state clearly whether 

 they came by a more direct route than exists at present. All 

 the other snails are considered by Dr. Pilsbry * to be waifs 

 and strays derived from Cuba and the Bahama islands, by the 

 agency of hurricanes, drifting trees and the like. 



I do not know why Dr. Pilsbry should make this reserva- 

 tion in favour of Drymaeus, as one of the species found in 

 southern Florida (D. dominicus) is also known from Haiti 

 and Cuba, besides the Mexican habitat. On the other hand, 

 we must not forget that Dr. Dall f discovered a number of 

 species of the land-snails Bulimulus and Cepolis in the 

 Oligocene Silex beds of Tampa in Florida. Both of these have 

 come from the south, for Bulimulus, though extinct in 

 Florida, still lives on the island of Fernando de Noronha in a 

 species almost indistinguishable from one of the Floridian 

 ones. Cepolis still inhabits Florida, but is not found else- 

 where in the United States. It has its headquarters in the 

 West Indies, and was a European resident, according to 

 Sandberger, in early Tertiary times. Of the land snail genus 

 Oxystyla, allied to Drymaeus, the species 0. undata has a wide 

 range in the West Indies, and is also known from southern 

 Florida. Yet the Floridian specimens both belong to varieties 

 peculiar to the peninsula. J Similarly, the Cuban varieties 

 of Liguus fasciatus are not the same as occur in Florida. 



The tropical forms of mollusks alluded to by Dr. Pilsbry 

 as inhabiting southern Florida are by no means the only ones 

 that have been collected there. The southern genera 

 Choanopoma, Truncatella, Microceramus, Cerion and Veroni- 

 cella (Vaginulus) have also entered this region. One of the 

 Urocoptidae lived in Florida already in Oligocene times, and 

 it is quite possible that Microceramus pontificus and M. flori- 

 danus, which are peculiar to southern Florida, have existed 

 there ever since. Among many groups of invertebrata long 

 specific persistence is much more common than is generally 

 realised. The fact that some of the Floridian species are 



* Pilsbry, H. A., " Origin of Molluscs of South Florida," p. 193. 

 t Dall, W. H., " Tertiary Fauna of Florida," Part IV., p. 1565. 

 I Pilsbry, H. A., "Manual of Conchology (Pulmonata)," Vol. XII., 

 pp. 109110. 



