112 EVOLUTION OF COLOR PATTERN IN LITHOCOLLETIS. 



minor ones, since the general plan of coloration has been already determined. 

 Where a group of species has branched early from the main stem, the individual 

 species within it will be found to be less closely related; the longer period of 

 time allowed for differentiation within the group has given opportunity for 

 greater divergence of the individuals composing it. 



In general, no effort has been made to discuss the minute characters separ- 

 ating the species. Such characters and their processes of differentiation are 

 more properly discussed later. 



Leaving out of consideration for the present the species of the subgenera 

 Porphyrosela and Cremastohomhycia, the main branch of the genus may be 

 divided, as has been mentioned earlier in this paper, into two natural divisions, 

 sufficiently distinguished from one another by the type of larva and by the 

 position with respect to the white fascise and streaks of the dark scales bordering 

 them. 



In the division whose larva in the later stages is of the normal cylindrical 

 type, when a dark margin occurs on but one side of a white mark, it is present on 

 the internal edge. In the majority of the species, this margin is the only one 

 present; in some species, however, external margins have developed adjacent to 

 some or all of the streaks. The external margin is, as a rule, considerably paler 

 and less complete than the internal one; in a few cases, where both are equall}^ 

 well developed, other characteristics will leave no doubt of the division to which 

 any species belongs. For convenience of reference, this division has been 

 designated Division I. The species are illustrated on Plate III. 



Several well-defined groups are recognizable. Some of these include a 

 considerable number of species, showing close intergradations and indicating 

 their origin from a common ancestor at a no very remote period. Other species 

 seem to stand apart, showing no very clear affinities with any of the existing 

 species. 



One group, comprising L. tiliacella (Fig. 1, PL III; Text Fig. 7), oregonensis,^ 

 affinis,^ tritcenianella (Fig. 5), ostensackenella (Fig. 7) and mariceella (Fig. 8) as 



typical forms, and fragilella (Fig. 3) and celtifoliella 

 Band I ^' ,. ^^[ ''' J, y\ viL (Fig. 4) as cxtremc deviations from the typical, is char- 

 acterized by the presence of at least two complete white 



_^ ,g transverse fascise, the first crossing the wing at about 



^ - -^ . , /' f. „ the basal fourth, the second near the middle. 



Fig. 7. Forewmg of L. lihacella. . . ^ 



In tiliacella (Fig. 7), the ground color is a very pale 

 golden; a spot at the base of the dorsal margin is white; the two fascise are almost 

 straight, the first but faintly dark margined. At three-fourths of the wing length, 

 there are two white dark-margined spots, corresponding in position to a third fas- 

 cia, very narrowly separated by pale golden scales which unite with a pale band 

 of the ground color beyond. Then follows a fourth white fascia, separated from 

 the apex of the wing by a few pale golden scales which mark the position of a band 



1 It was impossible to obtain figures of L. oregonensis, affinis, occitanica and alni. 



