Buddhist Dictionary of Pali Proper Names by G P Malalasekera
Ussillya
Ussillya:He was a resident of the Abhayagiri-vihāra.When the monks of this vihāra tried to introduce the Vaitulya heresy,he refused to be associated with them and went,with a few others,to Dakkhinagiri-vihāra.There they formed the Sāgaliya sect under a monk named Sāgala.P.L.C.66.