PARTULA GIBBA, GUAM. 75 
a slight but recognizable tinge of the characteristic color which is destined to extend 
and to intensify with age (fig. 27, plate 13). 
In castanea-purpurea purple-brown replaces the ruddy brown of its relative 
order (figs. 28 to 32, plate 13). All that is said regarding castanea-rubra holds true 
for this order, allowing for the difference in secondary color-distinction. 
It is not possible to confuse the castanea shells with any others, even though 
some of the darker mitella-rubra seem to approach somewhat near. The differ- 
ences are always discernible in the adult specimens, while the modes by which the 
two final phases in question are attained prove to be entirely dissimilar. In like 
manner the differences between castanea and phea are equally clear with an 
abundance of material before one’s eyes; and in this case also the two kinds are 
sharply contrasted in their partly grown stages (compare figs. 11 and 22 with figs. 
27 and 32, plate 13). 
It is undoubtedly significant that the few localities in which castanea occurs 
are also populated without exception by the next class, vespera. These two groups 
are not coextensive, it is true, but the relation of castanea to vespera in distribu- 
tion, and in some respects also in coloration, is closer than to any other class; at 
first sight the castanea type would seem to be nearer to the mitella-rubra or the 
phea class, but the contrary is the case. The castanea localities are not so far 
separated as their positions in the tabular arrangement would seem to indicate; 
Macajna, Fonte, and Aniguac are near one another, while Pago north, to the east of 
the first-named, is not really remote. Dededo is disconnected, it is true, and the 
presence of castanea at that locality when it is absent from the other collections 
of the Coast Central Region is an anomaly, due presumably to the small size of 
the representative series. 
vespera.—Ihe gzibba shells of the present class display the most delicate colors 
of all, and in recognition of their lesser brilliance, though undiminished beauty, a 
class name has been chosen which suggests the roseate and lavender tints of the 
evening horizon. 
In the vespera-rosea order, the general ground-color is corneous, overlaid to a 
lesser or greater extent with rose (figs. 33 to 38, plate 13). The interior is delicate 
rose-color, and the lip is always white. ‘The whorls of the spire, however, are very 
pale, verging toward whitish-corneous, but the extreme apex is very lightly tinted 
with pink. When the surface is decorticated (figs. 39 to 42, plate 13) the spire 
becomes practically white except at the very tip, and the body-whorl changes to a 
light rose-pink. The immature shells of this type are corneous at first (fig. 43, 
plate 13) and gain the pink color as a faint suffusion only later (fig. 44, plate 13). 
The first adolescent illustrated is from Macajna second and it can not be anything 
but a vespera individual, because unicolor and bicolor are both absent from that 
locality and because the young of the hooded mitella or of the deeply colored phea 
are distinguishable as such by the time they attain the equivalent size. 
The related vespera-cyanea shells are similar in their pattern, but they display 
lavender or lilac shades where rosea is pink (figs. 34 to 51, plate 13). The interior 
wall is similar to the outer wall in color; the lip is invariably pure shining white. 
