PARTULA GIBBA, SAIPAN. 105 
rubescens in each instance, or it may have migrated from the upland station to the 
coast. 
There is no need to develop the argument as to the absence of environmental 
causation for the observed diversities in colonial color-composition; the foregoing 
facts are sufficiently demonstrative as they are recorded. 
QUANTITATIVE CHARACTERS. 
When the several local collections are compared on the basis of their statis- 
tical characters they display marked differences that are somewhat unexpected in 
view of the short distances which separate their respective areas. The figures are 
here given for the range, mean value, and standard deviation of each of the standard 
characters in all of the representative series (table 51); owing to the large numbers 
available, the determinations are more reliable than in most of the local collections 
at Guam. The order of tabulation is geographical from north to south, and the 
changes manifested by the several characters in following that order are given with 
their probable errors in table 52. 
TABLE 53.—Partula gibba. Comparison of Saipan and Guam collections. 

MEAN VALUE. 

Saipan gibba 
Saipan gibba Guam gibba ; 
Character. | [No. = 2586] [No. = 2365] as compared with 
Guam gibba. 
Shell lengths iecsncseorios tees 17.0765+.0102 16.9966+.0102 +0.0799+ .0144 
Width, ANI Ge wens den eres|) »Le502962-..0076 11.7986+ .0078 + .2310+.0109 
proportions, per cent........ 70.3763 + .0316 69.3770+.0310 — .9993 + .0443 
Aperture length, mmai.ciwe 8 ook t 9.7461+.0057 9.6940 + .0057 +.0521+.0081 
NWIUGETE, AI cea.) os ere eases 7.2125+.0047 7.1178 + .0047 +.1047 + .0067 
proportions, per cent........ 73.8735 + .0300 73.3233 + .0302 + .5502 + .0426 
Aperture length +shell length, 
proportions, per cent........ 57.1991 + .0224 56.9199 + .0215 + .2792+ .0311 
STANDARD DEVIATION. 
Shell Jength Smit A-+ @piaaicie Peisiars 0.7702 +.0072 0.7364+.0072 +0.0338+.0102 
WICC tect vba crete. 0.5726+ .0054 0.5649+ .0055 [+.0077 + .0077] 
proportions, per cent........ 2.3862 + .0223 2.3336+4.0219 [+ .0426+ .0313] 
Aperture length, simi a2: a. ci eeu - atetes 0.4337 + .0040 0.4146+ .0040 +.0181+.0057 
WiICtlh MMi ao odeve ens abe. 6 0.3583 + .0033 0.3373 4.0033 {[+.0110+ .0046] 
proportions, per cent........ 2.26544 .0212 2.1777 4.0213 [+ .0877+.0301] 

Aperture length +shell length, 
proportions, per cent........ 1.6919+.0158 1.5500+ .0152 +.1419+.0219 

The general conclusion to be drawn from the facts is that the measurable char- 
acters vary without reference to environmental circumstances. ‘Taking the matter 
of altitude, it appears that the lowland series of Puntan Flores is the longest in 
average measure, but the shells of Chalankiya are also from the coastal plain, and 
they are the shortest of all, both in absolute dimensions and in the average figure. 
Conversely, the Sadog Tase shells from the high ground in the north are short, 
