WERNER MARCHAXD 177 



(fig. 19) the fused spots on segments one and two have become 

 more rounded and only on segment three a trace of the median 

 Hght area is left visible. The light borders of all abdominal seg- 

 ments may still preserve a trace of the original light pigmentation. 



Another series of changes may be observed in those species of 

 Chrysopswhere the lateral black spots do not fuse with the subdor- 

 sal ones but are reduced, and where the sul)dorsal spots themselves 

 remain apart, leaving a distinct light longitudinal band in the 

 middle of the abdomen. This process begins with ('. obsoletus 

 (fig. 20) with a pattern easily derived from that of C. vittatus 

 (fig. 16), but with the light background somewhat infuscated ex- 

 cept in the bright median dorsal area. In C. univittatus (fig. 21) 

 frequently the lateral spots have wholly disappeared, while the 

 subdorsal ones have been fused in the longitudinal direction, 

 forming two longitudinal black stripes at both sides of a yellow 

 longitudinal band. Sometimes the whole abdomen with the 

 exception of this light longitudinal band is dark infuscated, or 

 even black. In the sample given of C. lugens (fig. 22) a rather 

 varia])le species, we find the light median band itself in a process 

 of reduction ; while, at the same time, on segment two, traces of 

 the Hght subdorsal spots have been retained. 



The African and South American species of Chrysops show 

 essential^ the same stages of transformation as the North Ameri- 

 can species. Fig. 23 shows the abdomen of the African C. fus- 

 cipennis where the fusion of spots in the transverse direction has 

 been carried to an extreme, resulting in an almost wasp-like 

 l)anded pattern. The South American species C. omissus and 

 r. bulbicornis (figs. 24 and 25) represent rather primitive tj'pes of 

 pattern, not unlike the North American C. vittatus. In ('. omis- 

 sus a similar tendency to form ol)lique spots is visil)le as in T. 

 sujis, but the direction of the spots is the opposite in this case. 



I have not been able to extend this study to all the exotic fornix; 

 however, from the samples I have seen, I find no reason to depart 

 from this argumentation. The South American Eisenbeckios, of 

 which so many have been recently described by H. Lutz, show 

 usually a rather simple and therefore derived type of abdominal 

 pattern, not infrequently resulting in transversely banded forms 

 or such with entirely black or brownish aixlomen. An interesting 

 case is presented by Eisenbecki a infrcunacuJata (figs. 2f) and 27) in 



TRANS. AM. ENT. SOC, XLIV. 



