Specific differences in the Saws of 2 Dolerids. 429 
a method of representation gives a very inadequate idea 
of the really very characteristic appearance under a good 
microscope of the objects in question. It is not merely in 
the margins of the saws that striking and useful characters 
are to be found. Others, to my mind quite as important, 
and often more immediately recognisable, occur in con- 
nection with the surface (not the edge) of certain saws, 
and especially with the remarkable alternating elevations 
and depressions (“ridges and furrows,”) which invariably 
cross these surfaces diagonally, but must generally be 
ignored in an outline drawing. 
For instance, if the reader will compare for a moment 
the first and last of my figures (Plate XXIII, fig. 1, and 
XXV, fig. 12), he will see, no doubt, that the saws shown 
in them can be distinguished by their outlines only, but that 
they can be much more rapidly and confidently separated 
by the great unlkeness of their surfaces. The former 
shows a surface crossed by corrugations, which are armed 
with most conspicuous teeth or spines; while in the latter 
there are also corrugations, but they are edentate and 
comparatively characterless. 
Compare, again, figs. 1 and 5 of Plate XXIV, and it will 
be seen that though the outlines of their margins are not 
identical, a much more noticeable difference between the 
two saws is the presence in fig. 5 of great triangular tooth- 
like projections on the surface, which are altogether 
wanting in the other figure. 
It appears to me that, taking them as a whole and 
considering all their characters, we can divide the saws 
here figured into certain more or less definite groups ; which 
groups to some extent, but not altogether, correspond to 
subdivisions already pointed out by various authors as 
existing among these insects—subdivisions founded on 
external characters only and without any consideration of 
the structure of the saws. 
For instance, figs. 1, 2, 3, and 4 of Plate XXIII are all 
extremely different from any of those which follow them; 
and three of them at least (2,3 and 4) have a most peculiar 
and very similar common “ facies” of their own—resem- 
bling perhaps a little the saws of a very different Sawfly 
genus, viz. Tenthredopsis, but quite unlike those of any 
other Dolerids. Now these figures represent four out of 
the five species (the fifth genucinctus, Zadd., is unknown 
to me) which were singled out by Thomson, mainly on 
