288 VARIATION, DISTRIBUTION, AND EVOLUTION OF THE GENUS PARTULA. 
THE SHELLS AND THEIR VARIATION. 
The series of 1906 comprised 634 adults and 293 adolescent individuals, all of 
which are dextral (table 243). It is not until one penetrates to the higher levels that 
reversed shells are found, which accounts for their absence in Mayer’s collection 
and for Garrett’s opinion as to their scarcity. The shells fall into two principal 
classes, the wnbanded or “plain” and the banded, each of which is much diversified. 
In the former, which was considered the more typical by Pease, five well-marked 
subdivisions are recognizable: (a) a few shells displaying a yellowish-fleshy color 
(plate 34, figs. 14 and 15); (d) shells streaked with brown upon a light yellowish or 
whitish background (plate 34, figs. 16 to 18); (c) shells with darker background and 
more numerous strigations (plate 34, figs. 19 to 24); (d) still darker individuals with 
more crowded strigations (plate 34, figs. 25 to 27), and (e) shells with a deep-brown 
coloration with heavy but indistinct strigations that merge into one another, thus 
giving an appearance closely approaching that of the phea confluens members of 
the sinistrorsa, sinistralis, and crassa associations (plate 34, figs. 28 to 30). For 
practical purposes, (a) and (b) will be united into a group of so-called “light”’ 
shells, (c) will be treated by itself as a “medium” division, while (d) and (e) will 
be combined to form a “dark”’ class. 
Tape 243.—Partula otaheitana lignaria, Tipaerui Valley. 
Adults. Adolescents. 
Series. 
Per cent | Per cent Total. | Plain. | Banded. Per cent | Per cent 
Total. | Plain. | Banded. banded! ‘5 Mi linanacas 
1906, dex....] 622 419 
NOW CE. 5o0|} ile 74 
1909, dex.... 149 
1909, sin j 
Plain, number. Plain, per cent. 
| 
th Light.| Medium. |Dark. MAES Light.| Medium. | Dark. 
nt. .|| light. 
Very 
Thi dark. 
0.5 6.4 69.2 18.3 508) 
LoS 9.4 33.8 35.1 | 20.3 
Banded, number. Banded, per cent. 
Total. | Light. | Medium.| Dark. Light. Medium. 
1906, dex 
1907, dex 
The banded shells (plate 34, figs. 31 to 40) also fall into subordinate groups of 
“light” (figs. 31 to 35), “medium” (figs. 36 and 37), and “dark”’ (figs. 38 to 40) indi- 
viduals, according to the intensity and strength of the ground-color and markings, 
respectively. The characteristic and constant stripe is that which may be called 
median, although, like its counterpart in the single-banded affints, it lies rather to 
