(hex) y) 
cylindrico-conical trench or half-tube, which narrows gradually 
towards its apex; their sides are ribbed or corrugated, and 
are sometimes armed with spine-like projections, pencils of 
strong bristles, etc., ete. (See Plate Il, Fig. 10.) 
The “ saws,” as they are commonly called, viz. the lower (or 
anterior) pair of the two pairs which together make up the 
scalpellum, are not actually connate, either with each other, or 
with the supports ; but, like the latter, they are ‘‘ wired” to 
the insect’s abdomen, and also are connate with (indeed they 
seem actually to grow out of) a portion of its ventral surface 
—this portion not being chitinised any more than are the 
‘‘saws” themselves. They are completely separable from the 
“supports” by dissection, but, I believe, never are so separ- 
ated in the living insect. Whether ‘‘ sheathed ” or in action, 
their wire-like and shallowly sulcated upper margins cling to 
the under margins of the supports, along which they can slide 
backwards and forwards, on the principle of “flange and rail,” 
but from which they never actually part company. Unless, per- 
haps, at their inferior margins, it is impossible for them to be 
in actual contact with each other ; and I believe that, in fact, 
each makes cuts or scratches entirely by itself, independently 
of the other. These inferior margins are nearly always visibly 
serrate, or serrately undulate, in a particular point of view, 
viz. the lateral; but, as I have already said, the real cutting 
effected by them is probably due to other almost incredibly 
minute (and really saw-like) denticulations. Often the sides 
of the “ saws ” are armed with rasp-like processes, and usually 
obliquely corrugated—these corrugations more or less cor- 
responding with those of the ‘“‘supports”’; and it is the apices 
of these corrugations that form the projections commonly 
spoken of as ‘the teeth.” 
I must pass entirely over the special and often very para- 
doxical forms assumed by some of the above ten pieces in the 
terebrae of particular genera and species. The phenomena are 
extremely interesting, but it is simply impossible to discuss 
them adequately now ; and any one interested in the matter 
can easily examine them for himself. I will merely refer to 
various examples of them which are to be found in the Plates 
accompanying this paper. 
