PARTULA OTAHEITANA. 189 
addition, a type with broad zonal stripes makes its appearance, to be distinguished 
as the color-form zonata. Thus the colonies of the “eastern series” are characterized 
by the occurrence of dubia and zonata color-forms, in varying numbers. Proceeding 
out into the peninsula along the northern side, in Tehoro and Haavini Valleys one 
finds a new kind of particolored shell in which the colors are different on the two 
sides of the morphological sagittal plane; the special name given on this account is 
anomala, but the novel color-form does not predominate to such a degree that the 
term may be used as a subvarietal designation. Throughout the rest of Taiarapu the 
shells are little differentiated and resemble those of the eastern series especially; 
the colonies here are grouped as the “general Taiarapu series.” Finally in Oopu 
and Apirimaue, there are again typical affinis associations, to be called the Papeari 
colonies, from their district. 
THE NORTHERN SERIES—TUAURU TO PAPENOO VALLEYS. 
Tuauru VALLEY. 
The Tuauru colony, at the northward limit of the whole range, is large and 
flourishing and is sharply contrasted with the last colony of P. otaheitana amabilis 
in the near-by valley of Ururoa. Out of 366 adult shells, all but 3 are dextral, 
whereas in the Ururoa amabilis association only one dextral individual was found in 
a series of 345 adults. The dimensions of the aperture and its proportions are also 
distinctively different, but in coloration there is less contrast. 
Unbanded or “plain” shells predominate (73 per cent), and they are divisible 
into “light”? and “dark” groups, which occur in the general proportion of 2 to 5. 
Shells of the first group (plate 28, figs. 24 to 27) are usually marked with darker 
strigations upon a yellowish-brown background, although many are virtually uni- 
form in coloration without distinct strigation. The darker shells (plate 28, figs. 28 
to 34) grade from heavily strigated to solid seal-brown types. ‘The sinistral shells 
(plate 28, figs. 35 and 36) are unbanded. The banded shells (plate 28, figs. 37 to 41) 
all display a ‘“‘median” stripe and sometimes a basal clouding as well. The median 
band is usuaJly narrow, but sometimes it is doubled in width. In one specimen 
only (plate 28, fig. 42) the band is nearly confluent with the basal marking in such a 
way as to produce a bicolored appearance, thus simulating, but not equaling, the 
distinctive form of coloration termed anomala found in the far-distant valleys of 
Tehoro and Haavini. 
Wide variations in size and shape are displayed by the shells employed as 
illustrations. The statistical data (table 120) prove that the lighter plain group 
differs somewhat from the darker series; the differences are significant in shell 
width, shell proportions, possibly in aperture width, surely in the relations of the 
aperture to the whole shell and in tooth development. The banded shells agree 
closely with the others, saving only in the growth of the pillar-tooth. In general, 
the striped shells are more variable than those of the contrasted class. 
The plain sinistral shells as compared with the whole series of dextral individ- 
uals, or with only their plain division, are about the same in length, but are stouter 
on the whole and their apertures are larger, absolutely and relatively. At first it 
