22 VARIATION, DISTRIBUTION, AND EVOLUTION OF THE GENUS PARTULA. 
yet the material from the extreme localities mentioned is so similar as to render it 
probable that there is relatively little variation throughout the whole southeastern 
territory. 
CENSUS OF THE COLLECTIONS, GUAM. 
Nearly 4,000 adult snails of all species were collected in the entire series of 
localities, together with more than 1,500 immature individuals; the embryonic 
young and eggs dissected out of the bearing adults amounted to several thousand. 
The statistics given in table 4 record the varying absolute and relative numbers of 
the full-grown individuals, and the actual numbers of the adolescents as well. 
In dealing with the returns, it must be kept in mind that the figures specify 
the actual numbers taken, and that their significance varies according to the size 
of the collection. A consistent effort was made to secure representative series of 
snails from a large number of typical localities, and at places like Tarague, Bar- 
rigarda, Lolo, and Fonte the results were entirely satisfactory from all standpoints. 
In other instances, the purpose was to ascertain whether any snails at all were 
living in a somewhat divergent ecological setting; cases in point are Timoneng, 
where the open thickets along the roadside were under inspection, and Agat, where, 
the village environs harbored snails under circumstances that would ordinarily be 
prohibitive. Again, as at Tumon, only a few passing minutes were given to de- 
termine whether both radiolata and gibba were present. At other times, a heavy 
tropical downpour or other climatic influence might shorten the time of field-work, 
with only a small representative collection in hand. 
However, when all qualifications are made and all discounts allowed, certain 
general results emerge from the returns. It is unquestioned that P. salifana is 
sharply restricted in its habitat. Secondly, P. fragilis is local, for in spite of its 
wide ecological opportunities, it proves to be very scarce, except in the East Central 
Region; its occurrence in the Umatac area is quite extraordinary. Partula radiolata 
is less abundant relatively in the northern half of Guam, and more abundant in 
the same sense in the southern areas. Conversely, P. gibba exhibits exactly the 
opposite relationships. 
Judgment as to the variation of a species as regards its actual abundance in 
different localities must be based partly on factors which do not appear in the 
table. It is inevitable that the weather conditions at the time of collection and 
prior to such time could not be identical, and as the animals are very respensive to 
changes in the weather, the numbers of snails would be different even if the same 
period of time were devoted to securing them at all places. In the subsequent 
chapters dealing with the several species individually, particular attention is given 
to the problem as to the real abundance of a species or variety as distinguished from 
its apparent or relative frequency. 
COLLECTIONS FROM SAIPAN. 
While the survey of Saipan was unavoidably incomplete, yet its main purpose 
was accomplished with the collection at eight representative localities of large 
numbers of Partula gibba, the only species of the genus known to exist on the island. 
