638 ON SOME REMARKABLE AUSTRALIAN LIBELLULIN^E, 



note that of the two species of that genus inhabiting Australia,, 

 one (iV. stigmatizans Fabr.) possesses the heteromorphic or sim- 

 plified female only, while in the other (JV. oligoneura Brauer) the 

 change has extended to both sexes, so that the original intricate 

 venation is entirely lost. 



2. Loss of pruinescence, exemplified by specimens of the genera 

 Zyxomma and Orthetrum taken in Australia. 



3. Decrease in size; many examples of this might be given; see 

 Zyxomma obtusum, below. 



4. Simplification of colour-pattern; see Agrionoptera regalis 

 below. 



5. Contraction and intensification of dark pigmentation on the 

 wings. Neurothemis oligoneura Br., affords a striking example 

 of this; see also Camacinia Othello, below. 



The interesting problems connected with these peculiar 

 tendencies cannot be discussed in this paper, but the particular 

 facts relating to each species described in it will be noted in their 

 proper places. Seven species are now added to the Australian 

 list, of which five are new to science, while the hitherto unknown 

 male of Rhyothemis Alcestis Tillyard, is also described. 



1. Zyxomma obtusum Albarda. 



A single male taken by Mr. E. Allen, at Cairns, exhibits 

 remarkable differences from the type-form. It has absolutely no 

 pruinescence, and is considerably smaller than the type. It is 

 easily distinguished from Z. petiolatum Rambur (the only other 

 species of the genus found in Australia) by the shape of the 

 abdomen, which is short and rather thick, with segment 3 

 pinched. 



2. Rhyothemis Alcestis Tillyard. (Plate xiv., fig 2). 



(J. Wings very similar to those of the female, already described.* 

 Head and thorax as in Q. Abdomen slightly longer and less 



* These Proceedings, 1906, xxxi., p. 482. 



