EVOLUTION OF COLOR PATTERN IN LITHOCOLLETIS. 159 
In castaneeella (Fig. 88) and fasciella (Fig. 89), evolution has progressed 
more slowly on the outer edge of Band III and inner edge of Band IV; the 
median fascia remains almost straight, but the other white markings have 
almost disappeared. 
In two species, nemoris (Fig. 90) and gaultheriella (Fig. 91), the relations 
between the progressive changes in Bands II and III have been reversed. The 
tendency here is toward a fusion of Bands III and IV earlier than II and III, 
with the result that the second fascia is separated into opposite spots earlier than 
the first. Gaultheriella is the more advanced of these two species. 
In all of the groups whose evolution has just been traced, the action of the 
third process of evolution, namely, the retraction of pigment from the outer 
edges of the extremities of bands, has been of minor importance. In the evo- 
lution of four species, mediodorsella (Fig. 92), quercivorella ( Fig. 93), conglomer- 
atella (Fig. 94) and ulmella (Fig. 95), the characteristic longitudinal white streak 
has originated through the action of this process at the extreme dorsal end of 
each of Bands II, III and IV in sequence, followed by the extension of color 
toward the base from Bands III and IV, just within the dorsal margin. This is 
analagous to the process which has occurred in species of the first division of 
the genus, where it was observed that the most rapid extension of a band into 
the white streak preceding it took place just within the margin. These processes 
occur first near the base, then the bands more and more distad are involved. 
In mediodorsella (Fig. 92) Band IV has not yet been produced toward the base 
to obliterate the dorsal arm of the median fascia; in quercivorella (Fig. 93) this 
advance has been made. In conglomeratella (Fig. 94) and ulmella ( Fig. 95), the 
regressive changes have been extended to Band IV, which has shrunk away on the 
margin, allowing the white oblique streak to move proximally along the margin 
until it has united with the more proximal portion of the longitudinal streak. 
This theory of the origin of the longitudinal dorso-basal white streak is sub- 
stantiated by the variations in its width. It is widest at points correspond- 
ing to the original extremities of the white fasciæ, and narrowest immediately 
behind them. 
From the foregoing account of the evolution of the groups and species of 
Lithocolletis, it is evident that the general evolution of the pattern of the ground 
color may halt at any level and the species differentiated at this level constitute 
a natural group of species more closely related to one another than to any other 
species. The level at which evolution has come to a standstill is no absolute 
criterion of the age of the individual species within a group. A species with but 
few specialized specific characters in a group whose color pattern marks it as of 
recent origin may be older phylogenetically than one of a more primitive group, 
where the high degree of specifie differentiation attained marks it as of recent 
origin. It is to be expected that the most highly differentiated species, that is, 
those where the darker colors predominate both as regards ground color and 
markings, would be found in groups where the pattern of the ground color has a 
