44 UNITED STATES NATIONAL MUSEUM BULLETIN 27 6 



the midline of the body, and often covers much of the middorsal area. 

 It may be continuous from one segment to the next (fig. 350), broken 

 between segments (figs. 340, 375, and others), only faintly visible 

 (figs. 360, 381), or absent (figs. 342, 352, 382, 392, and others). If 

 absent, the dorsal area where it normally is found may appear as a 

 black stripe as in figure 358. The "subdorsal line" is a narrow area 

 at the junction of the subdorsal and supraspiracular areas which may 

 be absent, but if visible, usually consists of an irregular longitudinal 

 yellowish line that is often broken between segments as in figures 

 341 and 347. 



Some setal groups have distinctively colored areas around them or 

 distinctive groups of secondary setae surrounding them. Setal group 

 Dl usually is indicated conspicuously by the presence of a black area 

 surrounding it, and often appears as a pair of round black spots near 

 the dorsum of the larva (figs. 345 and 388 are good examples), with 

 one spot on each side of the middorsal area. More often the addorsal 

 area is black and obscures the black Dl spot (compare figs. 380-383). 

 Setal group D2, although difllicult to distinguish on most larvae, 

 may be surrounded by a small black spot (fig. 388), and sometimes is 

 marked by a small black area which projects downward from the 

 addorsal area on specimens which have black addorsal areas and blue 

 subdorsal areas (figs. 380-383). Setal group SD is also marked on 

 some larvae by a black mark of varying size and shape (fig. 374). 

 Setal group L2 quite often is surrounded by numerous secondary 

 setae which may be conspicuously tufted as in figure 345 and 391. 



Variability in Larvae of M. Calif ornicum 



If larvae of M. californicum from many different localities in the 

 West are examined, it soon becomes apparent that they are more 

 variable than larvae of the other species. In order to discuss and 

 describe this variation, the following special terminology has been 

 adopted for what seems to be a basic color pattern that has been 

 modified in various ways to produce the distinctive larval forms that 

 are found. 



This basic pattern is made up of the following components. The 

 middorsal area usually is blackish, but may be largely obscured by a 

 series of bluish-white dashes, one per segment. The dashes, if present, 

 range from large, almond-shaped marks (fig. 365) to small, thin lines 

 (fig. 381). The color of the addorsal area varies considerably from 

 one geographic region to another, but all specimens have a black spot 

 surrounding setal group Dl. This spot may be inconspicuous if the 



