64 VARIATION, DISTRIBUTION, AND EVOLUTION OF THE GENUS PARTULA. 
brown borders upon the upper whorls (fig. 25, plate 20) are more frequent than in 
other valley colonies; 4 are plain and darker (fig. 28, plate 20); 8 are variously 
banded, and in 5 specimens (figs. 34 to 36, plate 20) the banding resembles that of 
certain shells found to the south, but the other three (figs. 31 to 33, plate 20) are 
entirely different from anything discovered elsewhere; they are large and slender, 
in which respects they agree with the characteristic unbanded incrassa shells, but 
in the details of their markings they are absolutely unique. 
Of the lighter adults, 20 contained all together 24 well-advanced young, of which 
23 were light like their parents, while 11 were dark. One of the 3 dark adults 
bore 1 light-colored young shell; hence the two color types are not absolutely distinct 
in hereditary respects. Unfortunately 4 of the banded individuals were not gravid, 
while 3 others contained only eggs; the eighth with a banded shell bore 2 young, 
one of which was plain, while the other exhibited characteristic and distinct bands. 
TasLe 22.—Partula clara incrassa. Aoua Valley. 
Mean VALUE. 
Shell. Aperture. Length aper- 
ture + length 
Group. | No. ] shell, pro- 
Length. Width. Proportions. Length. | Width. Proportions. portions. 
mm. mm. p. ct. mm. | mm. p. ct. p. ct. 
Plain 55 | 15.3991 .0880) 8.5509 .0458| 55.5909 .2011) 8.3364 .0428) 6.1473 .0327| 73.7364+.2222) 54.1909 .2030 
Bands.... 8 | 15.8375=.2203) 9.0250+.0628) 57.1250 .4907) 8.6500 .1764| 6.4000 .0983| 73.7500 .6823) 54.2500+.5431 
Allyseanrys 63 | 15.4547 .0826| 8.6111 .0429) 55.7857 .1912) 8.3762 + .0444) 6.1793 + .0320) 73.7381 .2123) 54.1984+.1901 
STANDARD DEVIATION. 
Plain 55 0.9670 + .0622) 0.5033 .0324 2.2096 .1421) 0.4703 + .0302) 0.3597 .0231) 2.4417+.1570) 2.2308+.1434 
Bands.... 8 -9239+.1558) .2634+.0444 2.0577 = .3470) .7399= .1247| .4123+.0695| 2.8614+.4824| 2.2776+.3840 
Alltincae. 63 | 9727 + 0584) -5049 = .0303 DSS .5230+.0314| .3763+.0226) 2.4990=.1501) 2.2370+.1344 
Coming now to the measurable characters of the shell, it appears from the 
statistics (table 22) that the total length is astonishingly great, far in excess, indeed, 
of this dimension in parva, in the general population of the western quadrant, or in 
the whole population of the island. It is surpassed only in some of the shells from 
the eastern quadrant. ‘The width is not much greater, owing to the weak develop- 
ment of the flaring margin of the aperture. Naturally the form of the whole shell 
is narrow on account of the peculiarities mentioned, although other varieties found 
in the south show even greater departures from the average value in this character. 
The statistics referring to the banded group are not to be taken as entirely 
significant, because there are so few shells in this class. Furthermore, 5 of the light 
examples are much smaller than the other 3, and their ground-color is such as to 
place them with the “dark” plain group; the other 3 shells which exhibit the 
peculiar banded pattern have a much lighter color. This group, therefore, is not 
homogeneous, but on the whole its constituents are far longer and stouter than the 
series of plain shells. Its members are obviously only sporadic products of unbanded 
parents occupying various positions in the range of such a character as length; 
