34 VARIATION, DISTRIBUTION, AND EVOLUTION OF THE GENUS PARTULA. 
the shallow depressions between contiguous ridges that bear no streams or do so only 
in times of exceptionally heavy rains, as in the subsidiary sector behind Papeete 
(plate 152). 
In the tables and descriptions, the grades assigned to the several areas of collec- 
tion have been given on the basis of size and extent according to the best judgment 
of the present writer, although another observer might attribute different relative 
values to the valleys. Certain anomalies appear, it is true: Maruapoo, which is 
deep vertically and short in its inland extension, is put in the same class (fourth 
order) with Opiriroa, a longer and narrower valley of the southern quadrant; yet 
the areas inhabited by snails are more similar in character and extent than are 
the topographical features of these two valleys. Again, Papenoo is assigned to a 
series of first-order areas, although in extent it greatly exceeds Fautaua (plate 5a), 
Punaruu (plate 19), etc.; but it would scarcely be convenient to establish a separate 
order for this single greatest valley element of the island. In brief, the assigned 
grades may be employed as useful indices of size, even though they may be merely 
approximate. 
Tiarapu or Tahiti iti, the peninsula, is connected with the larger portion by a 
strip of land of low altitude about a mile in width, the Isthmus of Taravao. In 
its structure the peninsula reproduces on a smaller scale the features of Tahiti 
nui (plate 6a). On account of its lesser area the single primary valley, Tautira, 
communicates more readily with the elements of the second order, such as Haavini, 
Hototunu, etc., although even here the divides are of considerable height. 
The list of valleys from which Partule have been obtained is given in table 9. 
Doubtless there are others in which these snails occur, but the exigencies of the 
field investigation were such as to render the exploration of all of the lesser gullies 
impossible, especially in parts of the eastern quadrant and in Taiarapu. While it 
is conceivable that minor varieties might be brought to light through further inves- 
tigation, yet the list of 62 valleys undoubtedly covers the field satisfactorily and 
certainly gives a basis for a positive and extensive description of the conditions and 
situations of the forms existing in this island. 
The nomenclature of the areas of collection is not a simple matter, because as 
many as three or even four names for a single valley may be employed by the natives. 
Sometimes the name of a district will be applied to its single major valley, as Punaauia 
for Punaruu Valley; the name of the river is not always the same as that of the 
valley for which it is often employed; again, an inland area may be designated by 
the village that lies at its mouth. Furthermore, old names will be replaced by new 
ones, as in the case of Orofere, which is now called Faarahi, whereas Garrett speaks of 
it as Faahuaite. The names given in the present list are well known in usage, and 
no confusion need arise, because all valleys under discussion are definitely located 
in the charts accompanying this section and the verbal description given later; the 
essential matter to be safeguarded is such an accurate specification of the areas of 
collection that investigators of decades to come may identify the places whose forms 
are analyzed in the present monograph. 
