2 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. 62. 
made partly by myself, from the Malay Peninsula. With these last 
collections I have dealt or am dealing, in papers referred to where 
necessary in the sequel. 
Mr. Williamson did not confine his survey entirely to Burma and 
lower Siam in dealing with the Calopteryginae and Gomphinae, but 
increased the value of his notes by including in them remarks on other 
oriental species; in this I hope to follow him. But though it is evi- 
dent that I have at my disposal for study a very considerable amount 
of material, it will be evident equally that very much remains to be 
done before it becomes possible to assume that our knowledge of the 
occurrence and distribution of species constituting the oriental drag- 
onfly fauna is in any degree exact. 
A word as to the extension of this fauna will not be out of place. 
I regard it as occupying the following areas: The whole of British 
India, including Ceylon, but excluding Kashmir and Baluchistan; 
China south of the Yang-tze-Kiang; the whole of Indo-China; the 
Malay Peninsula and the Malay Islands as far as Flores; the Philip- 
pine Islands, the Celebes; Hainan, Formosa, and South Japan. In 
Flores and in the Celebes the oriental fauna meets and mingles with 
the Papuan; in China and South Japan with the Palaearctic. 
NOTES ON RELATIONSHIP OF GENERA. 
The present part deals with a subfamily, the Aeschninae, remark- 
able for the large size and superb powers of flight of many of its 
members. The group is a dominant one, and like most dominant 
groups it presents special difficulties to the systematist. 
The arrangement of genera here employed is largely identical with 
that elaborated by Walker (1912) in his Monograph of the North 
American Species of the genus Aeschna. His table of genera is prob- 
ably the best that can be constructed on our present acquaintance 
with the group, and any departures made therefrom in this paper are 
due to differences of opinion on matters of small importance. 
But the table can not be regarded as a satisfactory phylogenetic 
system. For this we must wait for the accumulation of much knowl- 
edge, morphological, developmental, palaeontological that is not now 
in our possession; and the present arrangement of the genera must 
be taken as a grouping according to the level of development to which 
they have severally attained; mainly in respect to the specialization 
of venation, rather than as an indication of lines of descent. 
As exemplifying the difficulties which beset the study of the phy- 
logeny of the subfamily I instance here the “‘dentigerous plate” of 
the female. 
This structure, a specialization of the sternite of the tenth abdom- 
inal segment of the female, is characteristic of the Aeschinae, and is 
not paralleled in any other Odonates. The specialization enables 
