240 ON SOME RARE AUSTRALIAN GOMPHINiE, 



green or yellow on a black or dark brown ground. In the genus 

 Austrogomphus the thoracic markings in particular are of great 

 value in determining species, very little individual variation 

 being found. B}^ referring to Plate xxii., fig. 11, the whole scheme 

 of thoracic markings may be readily understood. The 6gure is 

 diagrammatic, and represents the whole of the thorax, except the 

 prothorax, flattened out. Both sides of the upper surface or mes- 

 episternum(^)are shown; the whole being crossed longitudinally 

 by the mid-dorsal ridge or carina [h) ending in the cross-suture 

 called the interalar ridge (e). Besides this, on each side, well 

 forward, is a slanting transverse suture, the two together forming 

 the mesothoracic collar, or half-collar {g). On the mesepisternum 

 we have the following scheme of markings : — «, the border mark, 

 next the prothorax; 6, the half-oollar mark; c, the dorsal stripe or 

 band; d, the antehumeral stripe or band; and e, the mid-dorsal 

 line. In many species, h and c coalesce, forming a more or less 

 perfect representation of a figure ^'7"; the two together may then 

 be called the "seven-mark." Also the antehumeral stripe, which 

 is always narrow, is in some species broken up into a fine line 

 followed by a round or triangular spot. Coming now to the side 

 of the thorax, i.e., that portion lying below the humeral suture(i), 

 we have the large areas, separated by parallel sutures called the 

 upper or first lateral suture {j) and the lower or second lateral 

 suture (A;); these are the mesepimeron(^), metepisternum(C),and 

 metepimeron [D); there is also a small piece in front, near the 

 coxa, called the mesinfraepisternum i^E). Generally, over the 

 whole of this portion of the thorax the paler colour predominates, 

 with more or less regular dark lines or bands following the sutures. 

 But in some species these bands are very broad, and coalesce, 

 isolating large oval yellow spots. The complete thoracic scheme 

 alone is generally sufficient to determine the species to which any 

 specimen of Austrogoriijyhus belongs. 



For further specific differences, recourse must be had to sexual 

 characters. The abdominal characters of the males are so diverse 

 and peculiar that it is generally easy to determine them. The 

 females are more difficult to separate; but in any cases where 



