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XXII. Considerations on the Genus Tetracanthagyna Selys. 
By Ropert McLacutay, F.RS., &c. 
[Read December 7th, 1898. ] 
WHEN Mr. C. O. Waterhouse in 1877 and 1878 described 
in our “ Proceedings” and “ Transactions ” a grand dragon- 
fly, under the name Gynacantha plagiata, he acted, I 
believe, on my suggestion as to its generic position. In 
1883 my friend Baron de Selys, in his “Synopsis des 
AXschnines” (part i, classification), subdivided Gynacantha, 
Rambur, and proposed the subgeneric term Tetracan- 
thagyna for G. plagiata, being influenced principally by 
the conformation of the 10th ventral segment in the female. 
Prof. Karsch, in 1891, in his “ Kritik des Systems der Aesch- 
niden ”’ (in which he propounded a new scheme which, I 
venture to think, is a distinct step in advance), refused 
to recognise T'etracanthagyna even as a subgenus. 
Having to examine the materials available for a study of 
the genus, of which there are certainly several species, I 
arrived at the conclusion that not only is Tetracanthagyna 
valid, but also that its relationship to Gynacantha is per- 
haps not so intimate as has been thought; the mem- 
branule is more developed, the network less dense, and 
the abdomen more robust with, if I mistake not, a less 
strongly chitinous integument. A character which may, 
or may not, prove to be of importance, is the sinuate con- 
tour of the ventral surface, caused by constrictions ; nor 
should the very short styliform appendages of the female 
be overlooked. Even from the limited materials at present 
available, there are indications that the teeth on the 10th 
ventral segment of the female will prove to be somewhat 
variable, but probably individually rather than specifically. 
I propose to describe in detail what appears to be a 
new species, then to give in a tabular form characters of 
the described, and some new, species, ending by noticing 
some specimens the position of which seems uncertain. 
TRANS, ENT. SOC. LOND. 1898.—PARTIV. (DEC.) 
