158 EVOLUTION OF COLOR PATTERN IN LITHOCOLLETIS. 



and at the same rate, so that although the fascise between them have become 

 acutely angled, they have remained parallel. Macrocarpella (Fig. 74) and 

 cmcinnatiella (Fig. 75) have been differentiated at this level. These two 

 species are characterized by an unusual number of dark tipped scales; the 

 fascise are also internally dark margined near the costa. In saccharella (Fig. 

 76) evolution has continued farther, and other changes of a different char- 

 acter have resulted. There has been a slight displacement of the dorsal obHque 

 streaks toward the base; the first of these is brought into contact with the basal 

 streak. The costal portion of the first fascia has been replaced by the ground 

 color. 



In the other direction, where evolution has progressed at a more rapid rate 

 on the outer edge of Band III and inner edge of Band IV, than on the outer and 

 inner edges of Bands II and III respectively, the second fascia will be more 

 acutely angled and its arms more obhque than the first fascia. Such is the 

 condition in hamadryadella (Fig. 77), umbellularice (Fig. 78) and agrifoliella 

 (Fig. 79). In the first of these there is but little divergence in direction 

 of the two fascise, evolution in this direction having halted compara- 

 tively early. Specific differentiation progressed rapidly and dark pigment 

 developed along the outer as well as the inner edges of the bands. At this stage 

 regressive changes have commenced; the bands have shrunk away toward the 

 base, most rapidly at the extremities, but also in the middle, leaving behind them 

 the Hues of dark scales which marked their former outer edges. In umbellularice 

 and agrifoliella, progressive evolution continued longer, and the arms of the 

 second fascia are very oblique compared with those of the first. Specific differ- 

 entiation has continued longer in agrifoliella than in umbellularice; the recent 

 disappearance of the white fascia separating Bands I and II is shown by the 

 presence of black scales external to its normal position and by the occasional 

 presence of a few pale scales anterior to them. 



In all of these species characterized by two white fascise, there is a tendency 

 toward a disproportionate acceleration of the outward extension of the bands 

 along the cell, with the attendant result that the fascise are often interrupted at 

 the angle. 



In a collateral line of development, there has been an early acceleration in 

 the processes of evolution affecting the outer edge of Band II and the inner 

 edge of Band III. As a result Band II becomes fused with Band III over a 

 considerable space in the middle of the wing, at a period when III and IV are 

 still separated from one another by an angulated fascia. Fletcherella (Fig. 80), 

 arcuella (Fig. 81), betulivora (Fig. 82), australisella (Fig. 83), bethunella (Fig. 84), 

 chamber sella (Fig. 85), cervina (Fig. 86), platanoidiella (Fig. 87), castaneceella 

 (Fig. 88) and fasciella (Fig. 89) have followed this path of evolution. Chamber- 

 sella (Fig. 85), cervina (Fig. 86) and platanoidiella (Fig. 87) have been differ- 

 entiated subsequent to the first five species; fusion of Bands II and III has been 

 complete in the dorsal half of the wing. 



