Special Challos for Shabbos

The only special Challos mentioned in the Rishonim are the  Four Corner Challos & the Challas Oni.  There is no mention of Schlissel Challa   The נוהג כצאן יוסף quotes the רא"ש  “The Minhag on Erev Shabbos Hagodol  is to bake חלת עני from the whole Kehilla and distribute it to the עניים. From the time this Minhag was  neglected, a curse was sent on the grain.” The כל בו writes:  "There is a minhag for women to bake on שבועות a long bread with four corners (points) זכר לשתי הלחם  (looks like 2 loaves of bread or  because  מזל סיון is תאומים (twins)"