CHAPTER VI. 
PARTULA NODOSA Pfeiffer. 
GENERAL CONSIDERATIONS. 
Seven valleys of the western quadrant of Tahiti nui, situated in the districts 
of Punaauia and Paea, are inhabited by the beautiful species that was named Par- 
tula nodosa by Pfeiffer in 1851, on account of the nodular columella. In Garrett’s 
report of his careful field-studies, nodosa was described as occurring in Punaruu 
Valley only, but Mayer secured some noteworthy reversed shells of the same species 
in Maruapoo Valley, which is a small ravine immediately adjoining Punaruu to the 
south. In the course of the present research, P. nodosa has been taken from a 
series of seven areas, including the above, and in each of these it displays a number 
of characteristics that are peculiar to the colony of that particular locality. 
This species differs from P. hyalina and P. clara in its restriction to a compact 
sector, which, however, is not so contracted as the area inhabited by P. filosa. Its 
numbers are greater in nearly every valley of its range, in which respect nodosa 
resembles P. otaheitana; and in its differentiation within the borders of its field of 
occupation it also resembles the series of ofaheitana colonies existing in the same 
or in a similar series of valleys. Despite the narrow range and the relatively small 
number of colonies, the data at hand afford trustworthy evidence of recent migra- 
tion into one or more valleys previously unpopulated, and equally clear indication 
that a certain amount of mutation has taken place in recent years. 
Pfeiffer’s original description is as follows: 
“Shell perforate, conic ovate, rather solid, obsoletely decussate; chestnut-colored, 
ornamented with a wide white band at the suture, and often some other pale bands. Spire 
conic, acute. Whorls 53, a little flattened, the last about as long as the spire. Columella 
plicate above, deep within, then nodulose. Aperture subvertical, oblong, narrow; peri- 
stome outwardly scarcely expanded; inwardly provided with an acutely projecting white 
callus, contracting the aperture; margins subparallel, the right margin a little straightened. 
Length 16, diam. 8, aperture 6 long inside, 4 wide.” 
Pease, in 1866, described the ornamented shells of this species as Partula 
trilineata, which is subsequently (1871) made var. trilineata of Pfeiffer’s species. 
His description reads: 
“Cream color or yellowish horn-color, the spire usually reddish-brown, last whorl 
striped irregularly with brown, and encircled by three dark reddish-brown lines or bands; 
suture margined with white.” 
In 1899, Mayer explored Maruapoo Valley, where he found a colony of nodosa 
made up mainly (94 per cent) of reversed individuals. To this group he gave the 
distinctive name of var. sinistralis. Pilsbry points out the prior use of this term for 
another type of Partula, and substitutes var. /eva for Mayer’s designation. 
The descriptions in the literature and the early collections now in various places 
specify and exemplify two classes of shells which differ in the direction of the spiral 
and four principal classes that are distinguishable on the basis of color characters. 
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