Within the whorl group, the subclassification type double loop is
used for extension purposes only. In general classification it is
designated by the letter W.
The double loop consists of two separate loop formations, with two
separate and distinct sets of shoulders, and two deltas.
The word separate, as used here, does not mean unconnected. The two
loops may be connected by an appending ridge provided that it does not
abut at right angles between the shoulders of the loop formation. The
appendage rule for the loop applies also to the double loop. An
appendage abutting upon a loop at right angles between the shoulders
is considered to spoil the loop, while an appendage which flows off
smoothly is considered to leave the recurve intact.
The fact that there must be two separate loop formations eliminates
from consideration as a double loop the S type core, the
interlocking type core, and the formation with one loop inside
The loops of a double loop do not have to conform to the requirements
of the loop. In other words, no ridge count is necessary.
It is not essential that both sides of a loop be of equal length, nor
that the two loops be of the same size. Neither is it material from
which side the loops enter.
The distinction between twinned loops and lateral pocket loops made by
Henry and adopted by other authors has been abandoned by the Federal
Bureau of Investigation because of the difficulty in locating and
tracing the loops. Both types have been consolidated under the
classification double loop.
Figures 255 to 266 are double loops.
Figure 267 is a plain whorl. It is not classified as a double loop as
one side of one loop forms the side of the other. Figure 268 is a
plain loop. It is not a double loop because all of the recurves of the
loop on the right are spoiled by appendages.