268 VARIATION, DISTRIBUTION, AND EVOLUTION OF THE GENUS PARTULA. 
PARTULA OTAHEITANA CRASSA Pease. 
GENERAL CONSIDERATIONS. 
With the exception of the southernmost valley (Vaipaurii, which harbors the 
last representatives of sinistralis) the valleys of the western quadrant are inhabited 
by the third group belonging to the triple series of the south and west. The snails 
of this division are distinguished as Partula otaheitana crassa because Pease gave the 
last name in manuscript to certain characteristic specimens sent him by Garrett; 
crassa, however, is not an independent species, but is to be regarded asa primary 
variety of P. otaheitana allied closely to sinistralis and sinistrorsa, a relationship 
always to be kept in mind. 
The only description of crassa consists of passing comments in Garrett’s 
monograph, quoted previously. Its affinities with sinistralis and through this with 
sinistrorsa are indicated by its almost invariable reversal in coil, by the preponder- 
ance of shells with a dentate columella, and by the brown or yellow-brown ground 
color displayed by the shells of nearly all colonies. The principal color-classes 
conform to those of sinzstralis; in certain instances the plain phea examples are 
differentiated into the striata and confluens subgroups to a greater degree than here- 
tofore. The banded shells, still to be called cestata, are much less plainly striped. 
The distinctive qualities that will appear in the serial analysis of the colonies are 
few but important; among them, the prevalence of the strigated color-pattern and 
the close coiling of the shells are the most noteworthy. 
Within its territory, crassa is clearly differentiated into subordinate groups, 
some of which are so sharply distinguished as almost to be worthy of separation as 
subspecies of otaheitana; their respective areas of occupation are likewise distinct. 
Northward from Vaitupa, which adjoins Vaipuaru, the valleys as far as Orofere are 
inhabited by typical crassa colonies, to be considered collectively as the “southern 
series.” But in the next two areas—Aoua and Papehue—the shells present entirely 
different colonial characters in the way of color and form; undoubtedly these novel 
associations are descendants of an original crassa stock, but their peculiarities are 
such as to demand a definite taxonomic term, for which occidentalis is chosen on 
account of their western situation. Specifically, yellow and red colors approaching 
those of P. otaheitana rubescens are displayed, to the virtual exclusion of the usual 
crassa brown. Beyond their valleys, one finds typical crassa (“northern series’’) 
until Punaruu is passed and Taapuna Valley is attained, where again the basic type 
gives place to another subdivision, named P. otaheitana crassa aberrans on account 
of its divergence in color and form. In brief, then, the subspecies or primary 
variety crassa is differentiated intrinsically and geographically into crassa proper, 
crassa occidentalis, and crassa aberrans; the range of the first is interrupted by the 
territory of the second, and the area of the third lies to the extreme north beyond 
that of the last colony of crassa proper. The relative numbers assigned to the 
component color-classes, and the total numbers of adults collected in the several 
valleys, are given in table 223. 
