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XXIII. Palearctic Nemoure. By Kenneta J. Mor- 
Ton, F.E.S. 
[Read Oct. 3rd, 1894.] 
Puates XIII. and XIV. 
At the present time the Perlidz, and especially the 
smaller members of the family, occupy a prominent place 
amongst the less-known of European insects. Pictet’s 
treatise (“Histoire Naturelle des Insectes Névroptéres, 
Famille des Perlides, 1841”), now over fifty years old, 
may still be considered the standard of our knowledge 
of the family, and that work, in many respects of 
exceptional merit, naturally falls short of modern re- 
quirements as far as the separation of critical and closely 
allied species is concerned. 
I have now collected these insects for nearly three 
years, and have, at the same time, made them the sub- 
ject of more or less constant study during my limited 
leisure. The district in which I happen to reside has an 
exceptionally good representation of that aquatic insect 
hfe which belongs to running waters, and materials in 
Perlidx, including most of the British species, were thus 
easily obtained. ‘lhe results of an examination of these, 
in a fresh as well as a dry condition, have led me to the 
conclusion that the only reliable criterion for the separa- 
tion of the species is in most. cases to be found in the 
genitalia and accessory appendages of the ¢. ‘These 
parts have been too much neglected by previous 
writers on Perlidx, and in support of the conclusions I 
have come to regarding their value, I now offer the 
following notes on the species of the genus Nemoura, in 
which genus the appendages appear to be most highly 
specialized. These notes must be regarded as in all 
respects preliminary, but relating as they do to a 
neglected subject, it is hoped they may be of use. 
Monographic completeness is not yet possible, and has 
not been attempted. 
At the outset 1t was not my intention to do more than 
try to make known the species inhabiting the British 
Isles. ‘The expansion of the original idea is due to the 
TRANS. ENT. Soc. LOND. 1894,—PpaRT Iv. (DEC.) 
