270 
ORIGIN OF LIFE IN AMERICA 
from one another. Dr. Pilsbry divided them roughly into 
three groups, only one of which inhabits the Antilles. To 
trace the relationship of the various species to one another 
seems to be a task even beyond the powers of this distin¬ 
guished American conchologist. The minor sections being 
arranged geographically in Dr. Pilsbry’s work, it does not 
enable us to draw any conclusions as to their former dis¬ 
persals. One interesting fact, however, has been brought to 
light, which proves not only the antiquity of this family but 
the extraordinary persistency of specific characters among 
some of its members. The Oligocene Bulimulus americanus 
of Florida is practically identical with B. ridleyi, still living 
on the island of Fernando de Noronha. 
The genus Drymaeus (OtostomusJ, which is as difficult to 
classify as Bulimulus, has mainly a continental range. 
Only a few species live in the West Indies. Among these 
we likewise notice a remarkable persistency of specific 
characters. Drymaeus dormani, for instance, occurs in 
southern Florida, while the closely allied D. dominicus is 
resident in Haiti, Cuba, Florida, Yucatan, Nicaragua and 
Mexico. At the first thought we might feel inclined to attri¬ 
bute such a strikingly discontinuous range to accidental dis¬ 
tribution ; but a careful study of the whole family has im¬ 
pressed me with the conviction that we have to deal with a 
set of very ancient and very persistent types of mollusks. 
Even less satisfactory to identify than Bulimulus and 
Drymaeus are the Orthalicinae, another large group of Buli- 
mulidae. Dr. Strebel * has recently undertaken their revision, 
utilising several characters which had hitherto not been em¬ 
ployed in the discrimination of the species. It is an attempt, 
at least, to trace the complex relationship of the innumerable 
closely allied forms, although the author does not seem to 
realize the great antiquity of the group. His arguments in 
favour of wholesale accidental dispersal, even from western 
Mexico to the Antilles, are quite at variance with the lesson 
the study of the West Indian fauna has taught us. The species 
of Simpulopsis are mostly South American, but a small aber¬ 
rant group with smooth apical whorls is confined to Portorico, 
* Strebel, H., “Revision der Orthalicinen.” 
