REVISION MALACOSOMA HUBNER IN NORTH AMERICA 87 



have the forewings dusted with whitish-yellow scales which are usually 

 apparent to the unaided eye. Female tigris (females in figs. 161-175) are 

 a more intense reddish-brown than female constrictum, but also have the 

 forewings dusted with yellowish scales which are even more apparent to 

 the unaided eye. Also, the median area on the forewings of constrictum 

 and tigris is often darker than the inner and outer areas. Female disstria 

 are yellow-orange to orange-brown or brown, but the forewings are not 

 obviously dusted with scales of a different color than the background 

 color when viewed with the unaided eye. The median area of the fore- 

 wings is almost invariably lighter than the lines and about the same 

 color as the inner and outer areas. 



The separation of female disstria from female M. calif ornicum and M. 

 incurvum is normally not difficult because the lines on the forewings of 

 californicum and incurvum usually appear lighter than the ground color, 

 both Hnes are usually more bowed outward, and frequently have inden- 

 tations along the veins. Female disstria have the lines darker than the 

 ground color, they are more nearly straight, and tliey very rarely have 

 any indentations along the veins. There are some female californicum 

 (especially calif ornicum ambisimile (figs. 185—187), californicum californicum 

 (figs. 179-181), californicum pluviale (figs. 197-202), and californicum re- 

 censeo (fig. 190), however, on which the lines of the forewings appear to 

 be darker than the ground color. In these, the lines often will be border- 

 ed by a narrow line which is lighter than the ground color as in figure 

 186. This narrow line is never present in female disstria. If the narrow 

 line is absent in californicum, the lines on the forewings (especially the 

 inner one) are more sharply bowed outward than on disstria. 



In cases where identification based on the color pattern is doubtful, 

 female disstria can usually be identified by the sclerotized genital plate 

 (fig. 83). Females of the other species which are likely to be confused 

 with disstria have a nonsclerotized or only partially sclerotized genital 

 plate. 



The shape of the ovipositor of disstria is the most reliable means of 

 identification. It is most similar to that oi constrictum, tigris, and the west 

 coast and northern populations of californicum. Female tigris are easily 

 separated by the conspicuous indentation (in lateral view) between the 

 lobes of the ovipositor (fig. 84) which is absent in disstria (fig. 81). 

 Female constrictum are most easily separated by the distinct dorsal lobe 

 (fig. 86), and by the distinctive convergence (in posterior view) of the 

 ovipositor lobes below the anus (fig. 87). There is litde or no such con- 

 vergence of the lobes in disstria (fig. 82). Females of the west coast and 

 northern populations of californicum can be separated by a similar con- 

 vergence below the anus (fig. 92), and the different overall shape of the 

 ovipositor (figs. 91 and 97-99). 



