420 Aiiiialg of ilip South African. Musevm. 



specimens very narrowly whitish at proximal end. Immature males 

 similar to female, but black bauds of abdomen broader, very gradually 

 passing to mature colour ; vestiges of thoracic pattern often visible in 

 partly pruinose specimens. 



9 . Labium yellowish, median lobe, and sometimes a narrow median 

 line on side lobes black. Labium, face and frons yellow ; broad basal 

 black band on frons, extending anteriorly into furrow. Thorax and 

 abdomen light greenish-yellow with black markings ; cuneiform band 

 narrower dorsally, on median suture ; lines very close to humeral 

 suture, on humeral suture, half way to metastigma, on metastigma, 

 on second lateral suture, on metepimeron ; these lines, except the 

 sutural ones, mostly dorsally incomplete. Abdomen with broad, slightly 

 sinuate mid-dorsal band, narrow lines on lateral and transverse 

 cariuae, broader on segments 7-9 and confluent with dorsal black. 

 Wings slightly stained with gi-eyish yellow throughout ; deeper yellow 

 but very diffuse spots at nodus and variable yellow basal spot on 

 second pair to Aiiq^, Cit.q and end of membrauule in specimen from 

 Johannesburg. Legs black, with light yellow lines on external side 

 of femora. 



cJ , Abd. 27, hdw. 29, pt. 3 mm. 9 , 25, 29, 3-5. 



This is one of the characteristic Libelhdinae of the South African 

 fauna, though extendiiig northward to British East Africa. It 

 resembles strangely Trithemis Distanii, not only in colour but even in 

 o-enital structure of male, though H. dorsaUs has the wings com- 

 paratively more elongate than T. Distanii and their venation more 

 close. Males may further be distinguished by their hamule being 

 higher (especially the basal part) than in Distan.ti ; females and 

 immature males of Distanii show the black lines of thoracic sides 

 with a distinct tendency to longitudinal fusion, common to almost 

 all species of Trithemis; in H. dorsalis these lines are very sharply 

 defined and there is no indication of longitudinal fusion. Kirby had 

 described (1905) the genus as new under the name Mistholus, and 

 the male from slightly different individuals as M. avibiguus and 

 If. MarshaUi. The descriptions of Helothemis (Karsch) and of the 

 species dorsalis (Eambur) were made from the female. The highly 

 dimorphic sexes were united under the older name liy the writer. 



TRITHEMIS (Brauer, 1868). 

 A genus of wide distribution in tropical Asia, tropical and sub- 

 tropical Africa, the greater number of species African. Together with 

 Orthetrum it is the dominant African genus of Libellulinai; in number 

 of species and of individuals. 



