56 The Mechanism of Evolution- in Leptinotarsa 



Five specimens in the Jacoby collection in the British Museum, collected by 

 Hoge at Ventanas in Durango, Mexico, and recorded as L. decemlineata Say, 

 are in all respects like L. oblongata, but of nearly double the size, with the same 

 form and color-pattern system. I have never seen this type in nature, and do 

 not know that oblongata is found that far north. They may represent another 

 localized species of this group. 



Descbiption of Living Animals. 



Imago: Elongate, elliptical in outline, convex, distinctly and constantly 

 longer and narrower in proportions than any other species in the group. Above : 

 Epicranium and pronotum yellow, rarely tan or yellow-brown, marked with 

 black pattern. Epicranium rather regularly and uniformly punctate with 

 medium-sized punctations. Pronotum evenly punctate on lateral portion and 

 posterior border ; less punctate in median anterior portion. Mouthparts dark 

 yellow or yellow-brown, never black, eyes black; antennae, basal joints yellow 

 or yellow-brown, last six to eight black, faintly pubescent, sixth to eleventh 

 broad as long, twelfth truncate, conical; epicranium pattern, anterior lateral 

 epicranial spots fused, forming heart-shaped spot, lateral posterior epicranials 

 free, distinct, reaching to posterior border of eyes, rarely fused in median line. 



Pronotum, color-pattern, spots a' and a parallel, united a'— —a, forming 



U-shaped spot; b' and b sometimes fused entirely to a' and a. d', e', f and 

 d, e, f groups often completely united, forming dense black spot in the posterior 

 outer angle, and frequently fused anteriorly to b' and b. The modal condition 

 of the pattern is expressed by the formula : 



c' b' ■}-am+ b c 



e' + d' a' a d + e 



+ b +pm-i- f + 



The pattern is constant and typical of this species; scutellum brownish, 

 polished ; elytra pale yellow-white typically, rarely yellow or red, with anal 

 border black and five longitudinal black stripes ; second and third always united 

 posteriorly, sometimes also fourth ; all edged with irregular row of punctations. 

 Costal edge inflexed, flat or slightly concave, smooth, yellow, shoulder reduced. 

 Below: Yellow or yellow-brown, spots all present, variable amount of fusion; 

 legs, yellow or yellow brown, rarely red, femora mostly black or deep brown, 

 tibia ends black, tarsus black, femora sparingly punctate. 



Size: Smaller than muUitceniata or decemlineata, constant. Female larger 

 than male. 



Sexes: Female with sternal sclerite of last abdominal segment rounded com- 

 plete, smooth, and in male truncate, grooved, extending to near middle of plate ; 

 variable in male ; female also more robust than male and broader posteriorly. 



Food: Solanum rostratum or near relations, but will eat S. tuberosum, 

 8. el (Bagino folium, and S. hertwigi when other food is denied it, but they do not 

 thrive thereon and soon die out. 



Juvenile Stages. 

 (Tower, 1906, pi. 19, figs. 13, 14, 15.) 



Eggs: Pale yellow, oval, smooth, polished, laid in small bunches of 5 to 50, 

 on lower surface of leaves, rarely stalked; ventral side flattened and slightly 



