Geo. P Ide & Co., Ide Brand, “Stratton” linen starched fold collar with a lock front for men.

Stratton Collar by Ide.  The unusual looking curved extension on the wearers left side of the collar front helps to lock the collar into position which keeps it from bending with the wearer’s motion and pinching the skin of the neck or distorting the intended shape of the collar.

You can reproduce this collar using these scans as a pattern: