[Figs. 245-254]
Double loop
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 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.