222 VARIATION, DISTRIBUTION, AND EVOLUTION OF THE GENUS PARTULA. 
THE COLONIES OF TAIARAPU. 
The collections taken in the isthmus of Taiarapu possess an unusual degree of 
interest, both on account of their own peculiar qualities and also because this part of 
Tahiti was formerly uninhabited by otaheitana of the sinistrorsa series. ‘The latter 
point is clear from two facts: first, that Garrett describes the range of sinistrorsa 
as beginning with that valley in the southeastern part of Tahiti nui where affinis 
stops, 7. ¢., Apirimaue; second, that the map drawn by Garrett and published in 
Hartman’s paper omits s7nistrorsa from the peninsula, while it correctly locates the 
other species and varieties, some of which fall below sinistrorsa in numbers at the 
present time. Obviously, then, members of this group now under consideration 
must have entered Taiarapu in recent decades. Whether their present occupation 
of the new territory is due to their own migratory efforts, or has been brought about 
by human transport, can not be determined with certainty, for there are conflicting 
evidences on this matter. The primary fact is, however, that they now occur in a 
region which was devoid of them formerly; their peculiar features are scarcely less 
interesting than this fundamental datum. 
The range begins at the east with Vaiaaia Valley, the second topographical 
element from the end of the area of habitation of rubescens. Passing westward, 
the valleys are all occupied by flourishing associations of sinistrorsa as far as Haoma, 
which bears afinis only. Three color-forms are found in the whole area; in one case 
all three occur in a colony, in two cases only two, while in the remaining valley a 
single color-class is present. In their collective characters, the Taiarapu colonies 
are similar to the nearest ones of the main land-mass. The large size of the shells 
is their most notable feature. 
VAIAAIA VALLEY. 
The easternmost colony of sinistrorsa exists in Vaiaaia Valley, where about 
150 snails of all ages were taken, in addition to otaheitana affinis, clara, and hyalina. 
The shells fall into three color-classes, which, for the sake of brevity and clearness, 
will be given technical names. This procedure does not imply that any of these 
names has the value or significance of a term like afinis or sinistrorsa itself, which 
are group-designations; they are parallel to pallidior, etc., in the case of P. nodosa, 
and are to be used as brief substitutes for longer phrases or descriptions. 
Shells of the first class, apex (plate 30, figs. Io to 12), are bandless, and have basal 
and penultimate whorls of a light horny yellow color, while the upper whorls are 
lighter or darker brown with a purplish cast. In a few cases the spire lacks the 
dark color and is whiter than the lower part of the shell. This kind is represented 
in the collections of various museums, but its genetic relations to other types have 
never been defined, because no previous investigation has taken into account the 
data on the heredity of varietal characters. The second color-type, cestata, is the 
characteristic one of this primary variety; on a yellowish-horny ground-color three 
distinct revolving bands of a rich dark brown encircle the whorls (plate 30, figs. 
13 to 16). The sutural band is not wide, but the median stripe is invariably broad 
and zonate and is often more sharply defined than the others. At the base of the 
