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 plain arch would be an accidental whorl.

This subclassification also includes those exceedingly unusual

patterns which may not be placed by definition into any other classes.

Figures 269 to 271 are accidentals combining a loop with a tented

arch. Figures 272 to 276 combine a loop and a plain whorl or central

pocket loop. Figure 277 combines a loop and a double loop. Figure 278

combines a loop and a plain arch, so it is classified as a loop.

Figure 279 combines a loop and a tented arch.

Some whorls may be found which contain ridges conforming to more than

one of the whorl subdivisions described. In such cases, the order of

preference (if any practical distinction need be made) should be: (1)

accidental, (2) double loop, (3) central pocket loop, (4) plain whorl.

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