28 VARIATION, DISTRIBUTION, AND EVOLUTION OF THE GENUS PARTULA. 
of younger and older adults as distinguished by the absence or occurrence of 
decortication. The comparison reveals the fact that in the absolute measures of 
the whole shell and of the aperture, the former are slightly smaller; the explanation 
is that the lip continues to grow a very little after it is formed and reproductive 
maturity is gained. 
TABLE 6.—Partula salifana, Guam. Statistical description. 















Shell. Aperture. Length aper- 
‘ ture + length 
Series. No. shell, propor- 
Length. Width. Proportions. Length. Width. Proportions. tions. 
Range [class values]: mm. mm. pb. ct. mm. mm. p. ct. p. ct. 
Non-decorticated...| 7 17.15 —18.65 10.50 —11.10 57.5 —62.5 9.70 —10.30 6.85 —7.15 68.5 —70.5 53.5 —58.5 
Decorticated....... 10 17.75 —18.95 10.50 —11.70 57.5 —62.5 9.90 —10.90 6.85 —7.45 67.5 —71.5 54.5 —58.5 
Ala Ree one bee 17 17.15 —18.95 10.50 —11.70 57.5 —62.5 9.70 —10.90 6.85 —7.45 67.5 —71.5 53.5 —58.5 
Mean value: 
Non-decorticated...| 7 | 17.7929+.1255| 10.8714+.0573) 60.7857 +.4246) 10.0429+.0449| 6.9929+.0330} 69.2143 +.2244|56.3572+.3713 
Decorticated....... 10 | 18.2300+.0767| 11.1000+.0809| 60.9000 +.4392| 10.3600+.0715| 7.2600+.0387| 69.8000 +.3171|56.8000 +.2869 
AIL, cists diem ore uk oan 17 | 18.0500+.1505} 11.0059 +.0628} 60.8528+.3121) 10.2294+.0550| 7.1500+.0341} 69.5588 +.2134|56.6176 4.2305 
Standard deviation: 
Non-decorticated...| 7 0.4924+.0887| 0.2249+.0405|} 1.6659+.3002; 0.1762+.0317|) 0.1294+.0233| 0.8806+.1587| 1.4569+.264 
Decorticated....... 10 .3600 +.0542 3795 +.0572| 2.0591+.3105 .3353 4.0505 -1814+.0274| 1.4866+.2242| 1.3453+.2028 


eae ea ees 17 9202 +.1064 -3438 +.0444| 1.9079+.2207 -3365 4.0389 -2086+.0241| 1.3047+.1509| 1.4093 +.1630 

In the nature of the case the estimate of the fecundity of this species rests 
upon observation of only a single colony. Taking the facts as they appear (table 7), 
the reproductive rate of salifana falls short of that of the more abundant species 



of the island. The contrast between the non-decorticated and the decorticated © 
groups gives further evidence that the former are the more recently mature, be- 
cause their rate of productivity is lower. The differences are not great, it is true, 
but they are consistent. The colors of the embryonic young (table 5) have already 
been discussed. They are all dextral in coil. 
TABLE 7.—Partula salifana, Guam. Statistics of fecundity. 











Embryonic contents. 







Average 
for 
gravid. 
Per cent 
gravid. 
Average 
Records. Gravid. 
for all. 
Series. 

Eggs. Young. Total. 



Non-decorticated....... 10 8 18 3.00 
Deconicated sen are00s « 


By way of conclusion, it is interesting to compare P. salifana with P. gibba and 
P. radiolata of the same locality on the basis of the mean values or typical conditions 
of the several characters (table 8). The measures of the shell as a whole and the 
characters of the aperture show differences that are statistically significant in all 
instances, as judged by the probable errors of such differences. It is only in the last 
