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. Dali 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. 
f Dali, W. H., “Tertiary Fauna of Florida,” Part IV., p. 1565. 
J Pilsbry, H. A., “Manual of Conchology (Pulmonata),” Vol. XII., 
pp. 109—110. 
