310 RESUME. 
The three primary varieties distinguished as sinistrorsa, sinistralis, and crassa 
are more closely related inter se; they inhabit the southern-eastern, southern, and 
western valleys of the island. ‘Their shells are typically reversed, but dextral 
representatives occur in certain valleys, sometimes in the majority. The remaining 
sector of Tahiti, on the northwest, is occupied by /ignaria, which in certain respects 
has paralleled afinis in its differentiation from the pro-otaheitana stock. 
Each of the main sections of otaheitana is further differentiated to some degree, 
which in some cases necessitates the establishment of tertiary taxonomic divisions, 
as in affinis erythrea and crassa occidentalis. Again, the color-differentiation, like 
that of P. nodosa, has proceeded so far in such groups as affinis, sinistrorsa, and 
crassa as to justify the employment of special terms, orthographically distinguished 
for the several types, e. g., apex, cestata, and phea of P. otaheitana sinistrorsa and, 
P. o. sintstralis. 
Since its origin as such in a given area, a given primary variety has lost ground 
or rewon other territories of occupation, for the tides of immigration, in some 
instances at least, seem to have ebbed and flowed precisely as in the cases of P. 
clara and P. nodosa. 
Mutation is proven in several cases, both in an ancient area and in a recently 
occupied region; the mutant character can best be proven to be such in the genetic 
sense in the case of a departure in the mode of spirality. 
The attempt has been made in certain instances to analyze the phenomena of 
heredity in Mendelian terms. In the nature of the case, the difficulties are well-nigh 
insuperable, and the results can not be more than suggestive, in the absence of actual 
breeding experiments. ‘The offspring of a single snail are few in number, the other 
parent is unknown, the dominant member of a contrasted pair of characters is also 
unknown, while the proportionate numbers of DD, DR, and RR snails are not to be 
ascertained by a simple inspection of the adult population. Nevertheless a method 
has been devised which gives some insight into the mode of inheritance of con- 
trasted qualities, and which also makes it possible to designate one of a pair as a 
dominant to its alternative. To specify, the red color seems to be a dominant in 
relation to yellow in P. otaheitana rubescens and in P. otaheitana crassa occidentalis; 
the banded pattern seems to be dominant in relation to the absence of bands in 
P. otaheitana affinis and P. otaheitana sinistrorsa. ‘These conclusions are in accord 
with Lang’s experimental results on Helix. 
The congenital factors of variation seem to be paramount in comparison with 
the ‘“environmental”’ influences which affect the characters under consideration. 
Condensing the discussion to its briefest form, the conclusion is based upon certain 
negative and positive evidences. In the first place no differences in the environ- 
mental factors can be discovered that would account for the production of diverse 
but related primary varieties in different regions, or for the origin of a secondary 
form of a primary variety in one valley, while in the areas on either side the novel 
type does not appear. In the second place, the positive observations show that 
sometimes species X in the case of two neighboring valleys is the same, while 
species, Y may or may not be the same. It is merely an appeal to ignorance to 
