68 VARIATION, DISTRIBUTION, AND EVOLUTION OF THE GENUS PARTULA. 
one region or another. The figures for the inter-regional differences with their 
probable errors are given in table 28; it is true that the differences indicated are 
statistically significant in fewer instances than in the similar study of radiolata, 
but their essential meaning is identical. 
A detailed examination of the local series and of their differences may be 
carried out circumstantially to a lesser or greater extent, according to one’s interest 
in the facts of diversification in different areas. It is profitable to compare neigh- 
boring series in one and the same region with identical ecological conditions, to dis- 
cover the degree of difference that may exist, as in the case of the two Macajna or 
the two Presidio series; and it is also interesting to ascertain that with the passage 
from a low to a high level, or from a limestone territory to an area of volcanic nature, 
there are no invariable and consistent changes in the absolute or proportionate 
characters of the shells. 
Extracting a few specific data from the tabulations, the colony with the lowest 
average length of the shell is that from the inner Presidio, but the shortest individual 
is from Lolo (fig. 33, plate 13). The highest colonial average for this character 
is found in the Lonfit group, while the longest single specimen is from Ukudu 
(fig. 4, plate 13). The lowest colonial width is that of Fonte B and the highest 
is again that of Lonfit; the narrowest shell is from Lolo (again fig. 33, plate 13) 
and the widest measure is displayed equally by specimens from Tarague, Ukudu, 
Dededo, and Pago North. ‘The slenderest shell is one with a value of 61 per cent 
from Fonte B, and the stoutest specimens, disregarding absolute length, are from 
Asados and Ukudu, 76 per cent; but the lowest and highest colonial averages are 
those of Umatac Salonga and Orote respectively. The characters of the aperture 
and the relations of the aperture to the whole shell may be worked out in the same 
way. Plates 12 and 13 display many combinations of extreme and average con- 
ditions of the several quantitative characters of the shells. 
While individual fluctuations may occur in any or in all of the features under 
consideration, their existence does not invalidate the conclusion that environmental 
circumstances as such are virtually negligible in comparison with the genetic fac- 
tors that are ultimately responsible for the individual, colonial, and regional statis- 
tical characters, and for those of the whole collection taken as a comprehensive group. 
COLOR-CLASSES AND THEIR COLONIAL DISTRIBUTION. 
Were the material less ample and less diversified, it would be possible to deal 
concurrently with the qualitative and the quantitative characters of the color- 
types into which the species as a whole is differentiated; but, as in the case of radi- 
olata, it is necessary first to distinguish and describe the several color-classes, at the 
same time recording their geographical locations and frequencies. ‘The statistical 
characters are relegated to a later section—a procedure that is warrantable because 
such qualities are practically independent of color and coloration. It is true that 
the ranges of variation and the mean values may not coincide when two color groups 
are compared, but there is no consistent correlation between an average size and a 
particular kind of pattern like that claimed in the literature for Pease’s bicolor. 
