37 
psi were placed with tridens, and three specimens of tridens were in the 
series of psi. Lor greater certainty, I also examined two specimens of 
psi that might be taken for tridens, according to some criteria, and 
found that Mr. Barrett s and my own opinion of them was correct. 
I think, therefore, that anyone who handles a good number of 
specimens from any one locality, and probably if he has still more 
material, then from any locality, will rarely, if ever, be wrong in 
deciding which species any given specimen may be. 
I may, however, conclude as I began, by saying that no criteria 
can be laid down that will enable anyone without this experience to 
name a doubtful specimen, except with a large margin of probable 
error. My own experience is sufficiently defective, as regards the fine 
daik forms of both species found in the London district, to make me 
hesitate before pronouncing, and I should sometimas expect to prove 
wrong in my determinations of doubtful specimens, especially if 
females. 
The photographs presented herewith of the appendages of the two 
species (taken by Mr. F. N. Clark) show very well the difference 
of the spines of the claspers, and they also show a structure that 
is less frequently demonstrated, viz., the membranous structure that is 
eversible from the fiEdceagus, and that is armed with a beautiful 
arrangement of spines; it will be noticed that these spines are not of 
an identical arrangement in the two species, those of jm being all of 
a large, somewhat uniform, size, whilst those of tridens have an area 
in which they are distinctly smaller. It is, of course, accidental in 
mounting the specimens, that the ^Edoeagus is pushed out comparatively 
free of the other structures in the specimen of tridens, whilst it is 
amongst them so as to produce less clear outlines in that of psi. The 
other photo is from camera sketches of the clasps, and includes one of 
the spines of the allied enspis, and also tries to illustrate some of the 
variation that occurs in psi, there being equal variation in tridens. 
NOTES ON THE MICR0=LEPID0PTER0US FAUNA OF THE LONDON 
DISTRICT—TINEINA. 
(Head April 3rd, 1906, by ALFKED SICH, F.E.S.). 
The district of which this paper treats may be described as all that 
portion of the Thames Valley which lies between Charing Cross and 
Kingston. It is within the ten-mile radius from Charing Cross. The 
Thames here, flowing from Kingston, takes a serpentine course in a 
northeasterly direction. That portion of the district north of the river 
lies in the county of Middlesex, while the portion south of the Thames 
belongs to Surrey. In an area lying in such close proximity to the 
largest city in the world, it is quite natural tbat the Micro-lepidoptera 
should mostly be confined to the parks, commons, and other open 
