212 Dr. T. A. Chapman’s 
E. euryale may be assumed to exhibit the most normally 
developed type—presenting a base, body or shaft, a 
lobe or shoulder, and a hind process with a neck and head. 
This would describe the outline of the clasp, as viewed 
laterally, or at such an angle as will throw the spinous 
margin into profile along the edge. 
It is perhaps hardly necessary to say anything as to the 
difficulty in securing the same point of view in comparing 
different clasps, or in making the necessary allowance for 
any want of such exact correspondence. Having got over 
these difficulties myself, I may perhaps not make suffici- 
ent allowance for them in presenting the results so as to 
be clear to others. I have, however, endeavoured to avoid 
them as far as possible in the rough sketches that I pre- 
sent, so that they will support my statements without 
explanations as to the aspect shown, &c. These sketches 
are all taken with the camera lucida and to the same 
scale. 
I have adopted the method of preserving the pre- 
parations in balsam, on ordinary microscopic slides, with 
as little pressure as possible; a method that has 
several practical advantages, though it is not free from 
objection. 
I have not examined the appendages of every named 
variety, but have done so in nearly all cases, including all 
those where there seemed any possibility of specific 
differences ; H. margarita, a species founded by Oberthiir 
on a single specimen, and possibly a form of neoridas, is 
the only one I have not seen. In the case of all 
other species, I have examined material that has fairly 
satisfied me, in so far that, whilst in several instances I 
should have desired more and more varied material, I do 
not think the want of it has led me to any erroneous con- 
clusions. How far, of course, this confidence is justified 
remains to be proved, 
In arranging the species of the genus in accordance 
with the structure of the clasp, a certain group of species, 
with a definite clasp form, together with several others 
probably derived from this one, at any rate, unlike the 
remainder of the genus, is found to have a neuration 
differing from the rest; and, as the former species further 
are almost all of Asiatic and American distribution, whilst 
the rest are chiefly European, it seems best to divide the 
genus first into two sections. 
