THE SUBFAMILY LIBELLULIN^E. 257 



only. In many genera, especially in stout-bodied insects, the eighth segment is per- 

 foliate, that is, the lateral carina forms a semicircular membranous expansion on each 

 side. At the back of the eighth segment beneath we find a projection called the vulvar 

 scale, which is very prominent in many genera, and is sometimes bifid or trifid. 



Anal Appendages. — In the male there are two upper appendages, one on each side of 

 the extremity of the abdomen, which are generally curved downwards and then back- 

 wards, and are more or less pointed. They are usually about as long as the eighth 

 segment. There is also a lower appendage, curving upwards and usually pointed ; it 

 is sometimes nearly as long as the others, but is often shorter, and is sometimes bifid 

 at the extremity. The anal appendages of the female are usually very much shorter 

 than those of the males, consisting of a small pointed filament on each side of the 

 extremity of the abdomen ; in a few genera (Tramea Sec.) they are often as long as 

 those of the male. 



PAET II. 



Table of Geneka. 



In the present stage of our knowledge I think it would be premature to attempt to 

 subdivide the genera of Libellulinse into natural groups. I have, however, endeavoured 

 to tabulate the genera in such a manner as to allow of their easy identification, and to 

 arrange the genera themselves in something like a natural sequence. Even this, how- 

 ever, is not easy, from their great number and variety ; and in using the table it must 

 always be remembered that specimens will often occur which vary somewhat from the 

 usual characters of the genus, and hence may not always fall into the artificial divisions 

 of the table. Most of those anomalies, however, which have fallen under my notice 

 have been allowed for by duplicate entries in the table ; and every genus the name of 

 which occurs more than once is marked with an asterisk. As a rule, accidental 

 aberrations in neuration are confined to one side of a specimen, the other being- 

 normal ; and therefore when the two sides do not agree, both must, if necessary, be 

 compared with the table. 



For convenience, the term " cosmopolitan " has here been used to denote genera 

 occurring in Asia, Africa, and America at least, but does not necessarily imply that a 

 genus is also represented in Europe. 



Table of Genera of Libellulinse. 



1. A distinct concavity on the costa of the fore wings before 



the nodus. (2.) 

 No concavity on the eosta of the fore wings before the 

 nodus. (4.) 



2. Eyes not contiguous 12. Diastatops. S. America. 



Eyes contiguous. (3.) 



3. Tips of all the wings transparent 14. Palpopleura. Africa, China. 



Tips of the hind wings opaque 13. Potamothemis. S. America. 



vol. xii. — part ix. No. 2. — August, 1889. 2 q 



