232 VARIATION, DISTRIBUTION, AND EVOLUTION OF THE GENUS PARTULA. 
wherefore the collection of sinistrorsa was intentionally smaller. The area of col- 
lection was the same for both years. The gravid adults yielded 685 young snails 
to be used for the study of heredity; in sum, therefore, more than 1,700 sinistrorsa 
of all ages were obtained in Tenaire. 
The make-up of the adult material of the collection is given in table 176. 
The notable features are (1) the abundance and clear preponderance of dextral 
snails; (2) the lesser numbers of cestata as compared with apex in the sinistral 
division and with phea in the dextral group; (3) the extraordinary abundance of 
phea, which amounts to 67 per cent of the dextral series and only a little less than 
half of all. 
TasLeE 176.—Partula otaheitana sinistrorsa. Tenaire Valley. Numerical relations. 
Sinistral. Dextral. 
Color-class. 
No. of | Per cent of| Per cent.| No. of | Per cent of] Per cent 
adults. | sin. series. | of all adults. | dex. series.| of all. 
Elelo. to mogneo Dos 193 51.6 Pil 7 51 9.6 5.6 
cestatamieee 109 29.2 1133.3 124 23.2 13.7 
phesa ences) 75s 72 19.2 7.9 358 67.2 39.5 
WOM 650500 374 100.0 41.2 533 100.0 58.8 
Variation within the limitations of the color-class is unusually wide; apex is much 
as before (plate 31, figs. 1 and 2, 11 to 13), but cestata and phea present new features 
in addition to their qualities as seen in Titaviri and earlier. Aside from peculiarities 
in form and size, the cestata shells vary considerably (plate 31, figs. 3 to 7); some 
exhibit a terminal merging of the subsutural and median zones (fig. 3), and they 
grade through the typical patterns to narrow-striped shells like that shown in figure 
6, plate 31. Constriction of the median girdle gives a type with a zone of inter- 
mediate width (plate 31, fig. 7). All of these subordinate modifications are dis- 
played by dextral cestata as well, some of which are shown in figures 14 to 16, plate 31. 
The color-group called phea (plate 31, figs. 8 to 10, 17 to 19) includes shells with a 
modified coloration, and one which agrees with that specified as confluens (confluens) 
by Pilsbry (figs. 8, 10, and 17). Usually they are typically uniform in color, some- 
times of a very deep nature (fig. 18); the shell figured as No. 16 is a dwarfed 
mutant, which, in spite of its diminutive size, was that of a gravid adult. The 
embryonic shells (plate 31, fig. 20, a to F) display the adult types of coloration in 
both coils. 
A rigid and thorough-going analysis on the basis of the statistical data (table 
177) would involve (1) the comparison inter se of the three main color-classes in each 
mode of coil; (2) the comparison of sinistral and dextral groups of one and the 
same class; (3) the examination of the general relations of all sinistral to all dextral 
shells. A verbal transcript of the facts is unnecessary, for these are evident from 
inspection of the table. “The noteworthy points are (1) the remarkably close agree- 
ment of the three dextral classes, both in dimensions and proportions; (2) the 
smaller size of the directly coiled shells as compared with the reversed ones, although 
