les 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
another.

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.

[Illustration: 255]

[Illustration: 256]

[Illustration: 257]

[Illustration: 258]

[Illustration: 259]

[Illustration: 260]

[Illustration: 261]

[Illustration: 262]

[Illustration: 263]

[Illustration: 264]

[Illustration: 265]

[Illustration: 266]

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.

[Illustration: 267]

[Illustration: 268]

_Accidental_

Within the whorl group the subdivision type "accidental" is used for
extension purposes only. In general classification it is designated by
the letter "W" and for extension purposes by the letter "X".

_The accidental whorl is a pattern consisting of a combination of two
different types of pattern, with the exception of the plain arch, with
two or more deltas; or a pattern which possesses some of the
requirements for two or more different types; or a pattern which
conforms to none of the definitions._ It may be a combination of loop
and tented arch, loop and whorl, loop and central pocket loop, double
loop and central pocket loop, or other such combinations. The plain
arch is excluded as it is rather the absence of pattern than a
pattern. Underneath every pattern there are ridges running from one
side to the other, so that if it were not excluded every pattern but
the pl