DIAPERmi NORTH OF MEXICO — TRIPLEHORN 



379 



ation in each. The accompanying map (fig. 2) is the result of this 

 study. Percentages refer to the proportion of the total number of 

 specimens from each state in which the pronotum is red or reddish. 

 Fortunately it was possible to classify the pronotal coloration of the 

 vast majority of specimens as either red or green. The small number 

 of intermediate specimens and those which were teneral were excluded 

 from consideration. 



100% 



Figure 2. — Neomida bicornis (Fabricius): percentages represent the proportion of speci- 

 mens from each state having red pronota, based on at least 25 specimens from each state. 



The character of pronotal coloration forms a distinct north-south 

 clme. In the northern states and Canada, the entire population has 

 the dorsal surface greenish (rarely bluish), vfhile in the West Indies 

 and in the single specunen from Mexico, the pronotum is bright red. 

 Specimens from states between these two extremes fit rather closely 

 the expected curve of character gradient. 



There is a source of confusion that perhaps is not readily apparent. 

 It would have been more accurate to have collected data from specific 

 localities rather than from entire states. This would have clarified 

 the situation in such states as Texas and Florida, where the more 

 southern localities should show a higher incidence of individuals with 

 red pronota, but this was not feasible because there were too few large 

 series from specific localities available for study. 



Another source of confusion might be the tendency for collectors 

 within a given area to select against the particular form that is 



