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PACIFIC EXPLORATION: H. A. PILSBRY 
The most striking features of the second group in Polynesia and 
Hawaii are: (a) The absence of all the highly evolved continental 
groups of land snails. There are no Helicidae, no slugs, no carnivorous 
snails, none of the operculate Cyclophorid snails — in a word, none of the 
groups that have constituted the bullc of all known continental faunas 
since the Eocene, (b) The prevalence of groups that belong, by their 
relatively primitive anatomical structure, to early branches of the 
phyletic tree of the land snails. Some, such as the Amber snails (Suc- 
cinea), and the Endodonts, have relatives in Mesozoic continental 
deposits, and still form a small part of the modern continental faunas. 
Some, like the HeKcinidae, are presumed from their structure to be 
ancient groups, early terrestrial adaptations derived from the most 
primitive group of marine Prosobranch snails, (c) Another series of 
families, the AchatinelKdae, Amastridae, Partulidae, Tornatellinidae and 
Pupillidae, belong to a primitive group having pallial organs like the 
aquatic snails Lymnaea and Auricula. They form a primary division 
of the land snails called Orthurethra. One may compare their relation 
to the dominant groups of continental snails to the relation Monotremes 
bear to the placental mammals. 
This low group is represented on the continents by such minute 
forms as the Pupillidae and Valloniidae, which were present in essentially 
their modern forms in the Eocene, and still seem to exist by grace of 
their insignificance, occupying a station which no higher group has been 
modified to fill. 
In the island world, this primitive group has had a wonderful evolution. 
It comprises all of the large snails, and outnumbers all other groups. 
Shell forms have been evolved paralleling most of those of continental 
snails, except that up to this time no shell-less, sluglike form has been 
found. There are adaptations to all varieties of terrestrial and arboreal 
stations.^ 
The greatest variety of Orthurethra is in the mid Pacific; westward 
a few forms extend into islands also inhabited by some distinctively 
continental famihes of snails. Fiji is the extreme outpost of the latter. 
There they stop abruptly. The presence of this border of continental 
snails in the southwest Pacific has been looked upon by Hedley and others 
as evidence of former continental extension, while some zoogeographers 
attribute it to over-sea drift. The suggestion may be entertained that 
here a later fauna has been superposed upon an earlier. 
Where shall we look for the source of this unique Pacific fauna? 
It is known that on the continents the chief existing families of land 
snails were already established in the Eocene; and that many of the 
