74 VARIATION, DISTRIBUTION, AND EVOLUTION OF THE GENUS PARTULA. 
to a positive degree, lesser or greater. The inner surface of the shell is more 
reddened than the outside (figs. 4 to 6, plate 13). There is often some tinge of 
brown upon the lip (figs. 4, 6, plate 13). The white sutural border varies as in the 
other classes from narrow and vague (fig. 1, plate 13) to broad and distinct (fig. 8, 
plate 13); its contrast with the dark ground-colors renders it more conspicuous 
than in the light mitella and bicolor classes. 
The adolescent individuals (figs. 9 to 11, plate 13) exhibit a very light overtone 
of reddish brown upon the majority of the whorls, at the same time that they 
display the apical loss of color which is a distinctive feature of the whole phea 
class. Like the outer tints, the colors of the inner wall are pale at the outset and 
become intensified only later in life. 
The color-order distinguished as phea-purpurea comprises equally beautiful 
shells in which purplish brown takes the place of the ruddy brown of the foregoing 
(figs. 12 to 23, plate 13). The apex is lighter than the older whorls from early adoles- 
cence. ‘There is some difference between the Macajna second and the Asados associ- 
ations in the average depth of color; shells of the former grade to very dark purple- 
brown (figs. 13, 14, plate 13); their inner surfaces are likewise relatively deeper in 
tint (compare figs. 14 and 19, plate 13) and their colors develop earlier in adolescence, 
both within and without (compare figures 20 and 21 with figures 22 and 23, plate 
13). Decortication in this order as in rubra renders the shells more vivid in their 
coloration (figs. 18, 19, plate 13). 
In the matter of their geographical distribution, the phea shells are most 
interesting. Nine associations comprise pheza-rubra, and in 5 of these phza- 
purpurea is also present but in smaller numbers as the rule. The class is fairly well 
represented in the 3 localities of the Northeast Region, and in the eastern areas 
of the adjacent North Central Region; elsewhere it occurs only in the Macajna 
second collection, and in considerable relative abundance at that place. 
The few shells of the illustrations give no idea of the sharp contrast between 
this class and the others when large series of specimens are examined. Even the 
phea adolescent shells are clearly distinguished from those of all other classes, 
while in addition the differences between the two color-orders within the group 
are manifested almost from the embryonic period. 
castanea.—The primary color-class so denominated resembles phea in its 
general brownish tints and in the secondary distinctions of its two constituent 
orders, but it is none the less separate, and a different name is employed for the 
sake of description. Its numbers are few, and its members appear sparingly in only 
6 of the local collections. 
The castanea-rubra order (figs. 24 to 27, plate 13) is well represented by the 
specimen from Dededo (fig. 24, plate 13), which is ruddy chestnut-brown, without 
and within. The shells from Macajna second are lighter (figs. 25, 26, plate 13) and 
the first of these shows the effects of decortication in a more pronounced red color, 
verging toward pink. In sharp contrast with the phza shells, the members of 
this class and order display a darkened apex, without exception. And in the imma- 
ture shells also the apex is distinctly colored, while the rest of the shell displays only 
