ANTIQUITY OF SNAILS 
267 
Oligocene Period, generic differentiation probably dates from 
a much earlier time. Indeed, Dr. Pilsbry * is of opinion that 
the first radiation of the Antillean group of the Urocoptidae 
may have occurred on a Mesozoic Antillean land area. The 
succeeding Eocene depression, he thinks, isolated various 
branches of the existing stocks, western Cuba being pro¬ 
bably the first fragment to be dismembered. It was probably 
not until near the close of the Tertiary that continuity of 
land was restored with east Cuba. Haiti and Jamaica would 
seem to have remained united after both western and eastern 
Cuba had seceded. Finally, these islands were widely 
separated by the subsidence culminating at the end of the 
Eocene, or in the beginning of the Oligocene Period. This 
depression was again followed by an elevation in later Oligo¬ 
cene times, and it is likely that there was a transitory connec¬ 
tion between Jamaica and Haiti. Between the latter and 
Cuba the land connection probably lasted longer, thus pro¬ 
ducing the homogeneous distribution of several groups. It 
is likely, says Dr. Pilsbry, that during this mid-Oligocene 
elevation, the Haitian land included Portorico, the Virgin 
islands and the islands of the Anguilla bank, that is to say, 
some of the northern group of the Lesser Antilles. Dr. 
Pilsbry argues that the presence of large fossil mammals of 
South American type (Amblyrhiza and Loxomylus) in Plio¬ 
cene deposits of Anguilla demonstrates that the whole Carib¬ 
bean chain of islands was i.elevated into a ridge connected 
with South America during the Pliocene Period. He likewise 
expresses the opinion that the genus Brachypodella, one of 
the Urocoptidae, extended its range westward to Yucatan. 
Nevertheless, he contends that there is but scanty evidence of 
any direct land connection between the Greater Antilles and 
the mainland of Central America during the whole of Tertiary 
time. 
Thus, while differing from Dr. Simpson on several minor 
points, Dr. Pilsbry’s careful researches confirm his view, 
and that of many geologists, that originally there was a large 
area of land of which the Antilles are the last remnants, and 
that some time during the Tertiary Era almost the whole of 
* Pilsbry, II., “Manual of Conckology,” XVI., pp. xx.—xxiv. 
