2 VARIATION, DISTRIBUTION, AND EVOLUTION OF THE GENUS PARTULA. 
The following brief statement will indicate the nature and general bearing of 
the work: 
1. The present volume is concerned with the intrinsic nature and with the 
environmental relations of the species of Partula which exist in the Mariana Islands. 
Attention is focused directly upon the characters of the snails themselves, the 
diversities of such qualities, and the distribution of the several species and their 
distinguishable variations. In addition, all of the ecological conditions are con- 
sidered with regard to their possible effects upon the presence, nature, and dis- 
tribution of the snails. 
2. Field-work was carried out in Guam with an approach to complete explora- 
tion, and also to a partial extent in the northward island of Saipan. 
3. The Partula population of Guam consists largely of representatives of two 
species, P. gibba and P. radiolata, whose varying conditions are described as ex- 
hibited in the 39 areas where collections were obtained. The greater part of the 
present volume consists of the detailed description of these two species. 
4. The inter-island comparison of Guam and Saipan, 120 miles apart, is made 
on the basis of the one species which is common to the two areas, namely, P. gibba. 
5. Arare and unfigured species, P. fragilis of Férussac, has been found in Guam 
in sufficient numbers for a complete study. ‘This is the species called P. quadrasi 
in Pilsbry’s Manual, with the suggestion that it is Férussac’s lost kind. It is 
unique in the entire genus, as far as the author is aware, inasmuch as reproductive 
ability is manifested before the expanded lip of the shell develops. 
6. A new species has been discovered in Guam on the remote peak of Mount 
Salifan, and on account of the locality the new form is named P. salifana. The 
animals of this species are large and well-developed; yet, despite the fact that 
Guam has been a well-known collecting-ground for a full century, they have never 
before been found owing to the seclusion of their habitat. 
7. The question as to the originative value of the environment, as contrasted 
with congenital causes of differentiation, may be answered even more positively 
than in the case of the Tahitian study. All of the evidence proves that specific 
and racial diversification of the material under investigation is due to the operation 
of internal factors and not to external influences. 
