The Odonata or Dragonflies of South Africa. 407 



different from those originally described from equatorial West Africa 

 (pterostigma larger; cross-veins in sub-costal space yellow instead of 

 black ; yellow on thorax and abdomen more extended), it might 

 belong to a second species. But it does not seem advisable to name 

 a forin from a single immature female. 



9 (immature). Labium light yellow, a very broad black median 

 band. Laljrum yellow, black at anterior margin. Anteclypeus brown, 

 postclypeus light yellow. Frons black anteriorly, light yellow with 

 broad black basal line above. Vertex black, light yellow above. 

 Thoracic dorsum black with yellow markings; triangular spot in front 

 of ante-alar sinus, separated by a narrow black space from a broad 

 autehuuieral Ijand ; antehumeral bands slightly convergent dorsally. 

 Sides light yellow with two rather narrow black lines ; slightly in 

 front of metastigma and on second lateral suture. Metasterna chiefly 

 black. 



Legs black, first femora light yellow internally. Abdomen cylin- 

 drical, rather robust. Black with light yellow markings : sides on 

 segments 1-6, this colour widened dorsally at base of 4-6 ; 7-9 

 small lateral spots ; 1-3 sinuate yellow line on mid-dorsal carina ; 

 4-9 narrow line on mid-dorsal carina, slightly widened in distal third 

 of 4-6. Appendages and supra-anal tubercle light yellow. Ventral 

 surface black with marginal yellow spots. (Vvdvar scale not visible.) 



Wings hyaline, pterostigma" ochreous, sub-costal cross-veins light 



yellowish. Anq 9\-^\ ; / 0.0; ti 2.3; Cuq ^^-^ ; in front wing two 



rows of discoidal cells to level of bridge or slightl3' beyond (in left 

 wing but one cell in third series) ; in left hind wing two cells running- 

 through between M^ and Cu■^ (right side damaged). Arculus in front 

 wing at Anq;,, in hind wing slightly beyond. 



Abd. 18, hdw. 24!, pt. 2-5 mm. 



In a typical West African series adult males have considerably 

 more black on thoracic sides and the abdomen pruinose blue ; females 

 are similar on thorax to male, with yellow markings of abdomen 

 smaller ; a very mature specimen also with abdomen pruinose blue. 



ACISOMA (Rambur, 1842). 



The peculiar structure of the basal abdominal segments induced 

 Rambur to establish this genus, which is therefore one of the earliest 

 named genera in the subfamily LibeUulinae. Its affinities are 

 evidently with Diplacodes, of which it might be considered a specialised 

 branch. One form is common throughout tropical Asia, continental 



