The plain whorl consists of the simplest form of whorl construction
and is the most common of the whorl subdivisions. It is designated by
the symbol W for both general classification and extension purposes.
The plain whorl has two deltas and at least one ridge making a
complete circuit, which may be spiral, oval, circular, or any variant
of a circle. An imaginary line drawn between the two deltas must touch
or cross at least one of the recurving ridges within the inner pattern
area. A recurving ridge, however, which has an appendage connected
with it in the line of flow cannot be construed as a circuit. An
appendage connected at that point is considered to spoil the recurve
on that side.
Figures 194 to 211 are typical examples of the plain whorl type.
Figure 212 is, however, a loop, as the circuit is spoiled on one side
by an appendage.