PARTULA GIBBA, SAIPAN. 101 
these features are characteristic of the adolescent condition, and in this first group 
they persist even after the margin is developed about the aperture. The other 
group comprises “older adults,” with thicker shells and with definite coloration. 
When the two subdivisions are compared on the basis of the statistics of fecundity, 
the first contains relatively fewer gravid individuals, while the embryonic con- 
tents of such as are productive are smaller in number on the average. By way of 
concrete illustration, we may take the mitella and mitella-rubra color divisions 
of Chalankiya. Among the “recent adults,” the gravid snails amount to 6 per 
cent, while among the “older adults” they constitute about 99 per cent. The 
average contents of the first-named are about 3 eggs and young, while the figure 
is approximately 4 in the case of the latter. Hence the present species as it exists 
in Saipan constitutes another exception to the rule that the animals complete 
their shells and attain reproductive maturity at approximately the same time; 
and the added point of interest is that the exception is just the opposite of that found 
in Partula fragilis. 
TABLE 50.—Partula gibba, Saipan. Census of the collections. 


Number of adults. Percentage of adults. 
F ; 2 
g é o g : 8 No. of 
Series. 3 ; 5 3 3 : ‘ 3 adoles- 
re LT) & i = o as 
Total. 2 a & 3 3 3 a xe) i 3 3 2 3 2 | cents 
0 & = = a 2 ah ° As: = = a 2 ag 
2 g = £ 2 Ea hase, g 8 5 3 SOE i fre: B, 
5 5 E é 8 8 5 6 g E 8 § 
Puntan Plores........... 276 4 93 116 14 AO eae ae 1.45 | 33.69 | 42.03 IA OY ae BrP AC ae 58 
DIAG OM > LAB IE o lee icuie 3) ales 417 21% 72 £3 Tk toes < Gli Ae aes 64.99 | 17.26 es Wey tok LAN GS. lector atts V7 
Puntan Muchut........ 150 Z 76 29 20 yi Oa (A a ae 1255) DO SO HELO COST LO ROG |) LO aoa) Par stele 80 
Panaganams was oii 447 19 309 28 6 7 10 4.25 | 69.13 6.26 1.34 | 16.78 2.24 92 






COLOR-CLASSES AND THEIR COLONIAL DISTRIBUTION. 
In Saipan Partula gibba presents 6 color-phases in all, of which 2 are the 
primary classes unicolor and bicolor, essentially similar to those of Guam. The 
mitella and mitella-rubra types also occur again substantially as they were found 
in Guam. The remaining shells are referable to the color-class castanea; while 
they are further assorted into two orders which are distinguished by their respective 
ruddy and purplish tints, they do not conform in all details with the rubra and 
purpurea subdivisions of the class in Guam, and they are given the distinctive 
names of rubescens and purpurescens. The color composition of the several Saipan 
series is given in the census (table 50), which comprises the absolute numbers 
of adults belonging to the several classes and orders, their percentages also, and 
the total numbers of adolescents. 
The unicolor class displays considerable variation as regards the ground- 
colors (figs. 1 to 10, plate 14), What may be termed the median type is pale- 
