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 obhque and are 

 situated before the tip of vein 16 which in more primitive forms determines the 

 position of these white marks. The obhteration 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 scales of variable shape. 

 Of the species with apical dots, carycealhella (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 ostrycefolieUa (Fig. 23), 

 olivceformis (Fig. 24), ohscuricostella (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), cratcegella 

 (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. 



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 sexnotella (Fig. 39), ceriferella (Fig. 40) and obsoleta (Fig. 41). In ohsoleta 

 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- 



