150 PROCEEDINGS OF THE NATIONAL MUSEUM 



to 11 narrowing slightly progressively. In males about 0.55 of body 

 length, in females about 0.45. 



Legs black, compressed. Claws simple. 



There are two specimens of this species, labeled "Chile" and 

 "E. C. Reed" in the collection of the U.S. National Museum. 



Pyractonema nigripennis group 



(nigripennis, bifenestrata , obscura) 



Of the several hundred specimens received from Pefia, a series of 340 

 males selected without reference to the collecting station were mounted 

 and measured. They furnished a complete series at 0.25 mm. inter- 

 vals from 5 to 19 mm. long. Two more were 19.5 mm. In 147 females, 

 a nearly complete series from 6 to 22 mm. long was obtained, two 

 more being 24 mm. long. Plotting the number of male specimens 

 falling in each 0.25 mm. group showed principal maxima at 9.5, 12.5, 

 and 17 mm. lengths, and secondary maxima at 7 and 14 mm. The 

 females distributed somewhat similarly, but less definitely. There 

 were several pairs in copulation, and in each case the components 

 were of approximately the same size. 



On the basis of total length, it is possible to consider those from 

 15 to 19.5 mm. long (to 24 mm. in females,) as nigripennis: those 11 

 to 15 mm. long as bifenestrata; and those less than 11 mm. long as 

 obscura. This designation is arbitrary, of course, and involves some 

 overlapping between the species. Alternatively one must consider 

 that they all represent a single species highly variable in size. Olivier's 

 (1907) illustration of nigripennis gives a scale length of 14.75 mm., 

 and it might therefore be either nigripennis or bifenestrata by the 

 separation on total length proposed above. Collections made at the 

 same station and time frequently contained specimens of several 

 sizes. Study of the aedeagi showed that nigripennis , bifenestrata, and 

 obscura exhibited different patterns. 



In the initial separation of the specimens in this group, one series 

 was picked out by their relatively small and narrow pronota. These 

 specimens also proved to be intermediate in total length between the 

 larger specimens here called P. nigripennis, and the smaller P. obscura, 

 and constitute the majority of the specimens here classed as P. 

 bifenestrata. 



All of the specimens with short elytra, exposing up to 4 abdominal 

 segments, were females, and it seems probable that P. brevipennis is 

 a brachelytral form of the female in this group. The shortest elytra 

 were usually found in the largest specimens, but all gradations from 

 1 to 4 abdominal segments exposed were noted. 



In the original descriptions there is no essential difference other 

 than size between P. nigripennis, P. bifenestrata, P. binoiata, P. 



