MORGAN HEBARD 7I 



Ancon, C. Z., Pan., (Jennings), I (f . 



Panama, Pan., 1913, (Zetek), i o^, [United States National Museum]. 



The present series shows Httle variation, as is characteristic of 

 the present race. This is in strong contrast with the exceptional 

 amount of individual variation usually found in rufa occidentalis 

 Saussure. 



Ischnoptera rufa occidentalis Saussure (Plate IV, figures 9 and 10.) 



1862. I[schnoptcra] occidciilalis Saussure, Rev. et Mag. de Zool., (2), xiv, p. 170. 



[ 9 ; New [Orleans, Louisiana].] 

 1893. Ischnoptera coriformis Saussure and Zehntner, Biol. Cent. -Am., Orlh., i, 



p. 37, pi. iii, fig. 25. [ 9 , Nicaragua.] 



Tabernilla, Canal Zone, Panama, (Busck), i cf . 



Cabima, Pan., V, 19, 191 1, (Busck), i 9. 



Chorrera, Pan., V, 14, 1912, (Busck), i 9. 



These specimens show not only the highest development in the 

 present race as to size, but also in intensification of coloration and 

 in the diagnostic features of the male genitalia. It is therefore 

 evident that we ha\'e in Panama no intergradation between rufa 

 rufa and rufa occidentalis, but instead the most divergent type 

 developed in the latter plastic race, contrasting strongly with the 

 constant rufa rufa. 



The distribution of rufa occidentalis is now known to extend in 

 continental North America from the subtropical regions of the 

 Gulf of Mexico southward to Panama; that of rufa rufa from the 

 northeastern portion of South America westward to Panama and 

 northward throughout the West Indies. It is possible that rufa 

 originally passed from the West Indies to continental North Amer- 

 ica, and that the area where intergradation between rufa rufa 

 and rufa occidentalis would occur no longer exists. If so, we would 

 find in Panama the western limit of the distribution of typical rufa 

 and the most southern point reached by rufa occidentalis. In this 

 way alone do we feel able to account for the signal differentiation 

 between these two races in the same region. The convergence 

 in the large series of rufa occidentalis before us toward typical rufa 

 shows definitely that these two types represent races, and nothing 

 more, of one and the same species. 



The material here studied of rufa occidentalis is in every way 

 similar to specimens from Pozo Aziil, a locality in the southwestern 



MEM. AM. ENT. SOC, 4. 



