Schiballa .g. per .sk. melius scribitur et per .y.psilo sunt stercora dura rotunda.
Schiballa ACD ef | Schicala B
y psilo AC e | y psilon BD | y psillo f
Schiballa is a Greek word, but it would be better written with 'sk' and with y psilon. These are hard and round droppings.
Greek σκύβαλον, pl. σκύβαλα, means "dung, manure, excrement; refuse, offal".
Simon is obviously aware that a more etymologically oriented transcription would be Skyba(l)la.
Greek υ = 'y' was at that time already pronounced /i/ in Greek and in Medieval Latin.