J2 VARIATION IN LEPTINOTARSA. 



Individual Variation in the Color Pattern of the Epicranium. 



Variation in the color pattern of the epicranium in the lineata group. The 

 color pattern of the epicranium, while simple, is no less variable than that 

 of the prouotum. It consists of two spots placed just laterad of the median 

 line and two placed at the outer posterior angle behind the eyes (text-fig. i). 

 In the variations of this area a range is exhibited from complete melanism 

 to total xanthism and albinism. On plate 15, figs. 1 to 7, is shown the range 

 of variation found in L. multitceniata and L. me/anot/wrax (fig. 8). This 

 species shows an almost complete series from one extreme to the other. 

 Only at the xanthic and albinic end of the series are stages wanting to make 

 a complete series in this one species. These are supplied, however, by its 

 northern modifications, intermedia and dccemlineata, which complete the 

 series (plate 15, figs. 12 to 16). The range of variation found in L. decem- 

 lineata, as shown in these figures, is considerably less than that found in 

 multitceniata, but greater than in the other species of the group. The varia- 

 tions of undccimlineata are shown in figs. 9 to 11, plate 18. 



The direction of the fusion of the spots on the epicranium is well shown 

 in figs. 1 to 6. In fig. 1 all of the spots g, h, i and g' , //', i' are distinct 

 pigment areas. In fig. 2 are shown the first steps in the fusion, the union 

 posteriorly of g and g' to form a V-shaped spot and the medianward exten- 

 sion of h and //'. This process is continued in fig. 3 until g and g' have 

 formed a heart-shaped spot in the center of the epicranium, which becomes 

 more pronounced in fig. 4. In fig. 5 is shown the caudalward extension of 

 this spot until it meets the medianward extension of // and //, and all combine 

 in the posterior median border of the epicranium. Further variation con- 

 sists in the lateralward and cephalward spread of the spots g and g' and // 

 and kl, as shown in figs. 5 to 7. No other variations of the color pattern of 

 the epicranium of the lineata group are known, excepting rare abnormal 

 conditions of asymmetrical variation caused by unequal development upon 

 the two sides. These, however, are due to accidental causes acting during 

 pupation, and are of no interest in this connection. 



The proportion of light to dark color in the epicranium of the lineata 

 group is of interest, showing, as it does, a series of gradations much like 

 that found in the pronotum. It has been convenient to establish ten classes 

 to represent these gradations, class 1 (plate 15, fig. 12) indicating total 

 xanthism or albinism and class 10 (plate 15, fig. 8) total melanism. The 

 variation in this character of the different species in the lineata group has 

 been studied by sedations, which can best be presented in the form of tables. 



