154 EVOLUTION OF COLOR PATTERN IN LITHOCOLLETIS. 
group, there has also been a retraction of pigment from the outer edge of 
Band III, and at the same time, the extremities of Band IV have been produced 
toward the base so that the first pair of white streaks are very oblique and are 
situated before the tip of vein 15 which in more primitive forms determines the 
position of these white marks. The obliteration of the first white costal streak 
has not been attained in all the forms which reached this level before evolution 
in the pattern of the ground color halted and species differentiation began, 
since it is preserved in some species and lost in others. 
Within this group the development of the dark markings in the apex has 
taken two different directions; the black marking in the apex may take the form 
of a round apical dot, or of a streak or patch of black seales of variable shape. 
Of the species with apical dots, carywalbella (Fig. 21) lags somewhat behind the 
other species; the suffusion of the base of the wing with pale yellow is not 
yet complete, but the first costal streak has been lost. Development has been 
more rapid toward the costa than in the dorsal half of the wing; the converse is 
true for rileyella (Fig. 22) where the first white costal streak remains. In 
conformity with the principle that within a group a darker ground color and the 
presence of dark markings indicate a higher phylogenetic position, the sequence 
of the remaining species with an apical dot will be ostryefoliella (Fig. 23), 
oliveformis (Fig. 24), obscuricostella (Fig. 25) and kearfottella (Fig. 26). In the 
last two species all trace of a white spot near the base of the dorsum has 
vanished. 
Of the species characterized by more or less irregular patches of black scales 
in the apex, populiella (Fig. 27) is probably the most primitive from the point 
of view both of color areas and markings. Among several of the species, 
namely, diaphanella (Fig. 28), salicivorella (Fig. 29), deceptusella (Fig. 30), alni 
(Fig. 31) and alnicolella (Fig. 32), the pair of streaks in the middle of the wing 
are not very oblique, that is, there has been a more restricted action of the last 
two of the three processes of evolution than is observed in the five following 
species. In ledella (Fig. 33), incanella (Fig. 34), scudderella (Fig. 35), crategella 
(Fig. 36), malimalifoliella (Fig. 37) and propinquinella (Fig. 38), these streaks 
are very oblique. 
If evolution of the pattern of the ground color, instead of halting at the 
level of the preceding group of species, proceeds farther, it takes place in two 
directions. sd 
1. The base of the wing may be uniformly suffused with ground color, so 
that no white streaks remain when evolution ceases, and therefore no dark 
markings develop. The configuration of the ground color in the remainder of 
the wing has remained constant during these changes. This is the condition of 
affairs in seznotella (Fig. 39), eriferella (Fig. 40) and obsoleta (Fig. 41). In obsoleta 
the pattern remained fixed for a short time, and the development of dark pig- 
ment in the scales adjacent to the white streaks was initiated, then the exten- 
sion of all the bands toward the base was resumed, checking further develop- 
