EVOLUTION OF COLOR PATTERN IN LITHOCOLLETIS. 159 



In castanemella (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 gauUheriella (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 earher than 

 the first. GauUheriella 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, mediodor sella (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 mediodor sella (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 obhque 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 fasciae, 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 specific 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 



