Nicene and Post-Nicene Fathers, Ser. II, Vol. XIV:
The Canons of the Synods of Sardica, Carthage, Constantinople, and Carthage Under St. Cyprian, Which Canons Were Received by the Council in Trullo and Ratified by II. Nice.: Canon CXXIII

p. 502 Canon CXXIII.  (Greek cxxiv.)

That if a bishop neglects his diocese he is to be deprived of communion.

If in the mother cathedrals a bishop should have been negligent against the heretics, let a meeting be held of the neighbouring diligent bishops, and let his negligence be pointed out to him, so that he can have no excuse.  But if within six months after this meeting, if an execution was in his own province, and he had taken no care to convert them to Catholic unity, no one shall communicate with him till he does his duty.  But if no executor shall have come to the places, then the fault shall not be laid to the bishop.

Notes.

Ancient Epitome of Canon CXXIII.

A bishop who spurns the care of heretics, and if after being warned he continues for six months in his contempt, and has no care for their conversion, is to be excommunicated.

This is Canon xv. of Carthage, a.d. 418.

Johnson.

So [i.e. “Metropoles”] I turn matrices cathedræ.  I know indeed there were no fixed ecclesiastical metropoles, in Africa; but they had civil metropoles called by that name, can. 86, (89) which see.

Of these officers [i.e. “Executors “] see can. 97 (100).