SUMMARY. 115 
RESUME OF CHAPTER IV. 
Férussac gave no figures of the form described by him in 1821 as P. fragilis, 
- but his terse description leaves no doubt that his specimens belonged to the species 
now found mainly in the northern part of Guam in very small numbers. In 1894 
von Moellendorf described the same species as P. quadrast, also without giving any 
figures of the shell or of the animal. The snails are small, and their shells are thin 
and diaphanous; they are most abundant in the northern region where the rock is 
limestone, but the geological circumstance has no more relation to the texture of 
the shell in this case than it has in the contrasted instance of salifana. The body 
within is boldly maculated and its colors may be seen through the shell; hence the 
appearance of the animals in life is very different from that of any other Guam 
type. The upper coils are tumid and the last whorl is swollen somewhat as in 
P. turgida of Raiatea in the Society Islands. 
But the most notable peculiarity of the species is its precocious reproductive 
activity. In no other known species are eggs formed before the flaring lip about 
the aperture is constructed as the conventional sign of maturity; in fragzlzs, all of 
the animals with completed shells bore young and eggs, while in addition all of 
the “adolescent” individuals over 12 mm. in length were gravid, despite the fact 
that their shells lacked the finished lip. Finally, in contrast with its associates 
of the Mariana Islands, fragilis produces egg-capsules whose walls are fully im- 
pregnated with calcareous substance, as in the prevalent Tahitian species. 
RESUME OF CHAPTER V. 
Partula radiolata is a well-represented species which now spreads throughout 
nearly all parts of Guam; hence it is available for a study of geographic distribution 
as the foregoing species were not. Its proportionate numbers are not the same in 
all of the local associations, but its variations in frequency are not related in any 
discoverable manner to ecological conditions. 
The statistical characters of the individual colonies and of the combined 
regional populations are fully recorded so as to give a sure basis for future studies 
of a similar kind which may disclose the occurrence and nature of any evolutionary 
changes during the interim. The colonial qualities vary without any relation to 
external circumstances; under the identical conditions of contiguous areas, the 
radiolata groups may show marked differences, while similar statistical features are 
displayed by the members of colonies which thrive in diverse ecological regions. 
Variations in color and color-pattern are even more striking than in the measur- 
able characters of the shells. Six color-groups are now found in Guam and three 
of these are newly distinguished; they are given distinctive names, not of taxonomic 
significance, which refer to their characteristic colors or patterns. The local asso- 
ciations of radiolata differ much among themselves as regards color composition, 
and in two ways; the kinds of color-classes present may be very unlike even in 
neighboring associations, while in addition the proportionate numbers vary greatly 
even when the same kinds are present in comparable colonies. It is even more 
evident than in the case of the structural qualities that the environmental circum- 
stances are negligible as factors of the individual and colonial color characters, and 
