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 CXVIII

p. 500 Canon CXVIII.  (Greek cxix.)

How bishops as well Catholic as those who have been converted from the Donatists are to divide between themselves the dioceses.

So, too, it has seemed good that if a bishop has been converted from the Donatists to Catholic unity, that equally there should be divided what shall have been so found where there were two parties; that is, that some places should pertain to one and some to the other; and let the division be made by him who has been the longest time in the episcopate, and let the younger choose.  But should there be only one place let it belong to him who is found to be the nearer.  But should the distance be equal to each of the two cathedrals let it belong to the one the people may choose.  But should the old Catholics wish their own bishop, and if the same be the case with the converted Donatists, let the will of the greater number prevail, but should the parties be equal, let it belong to him who has been longest bishop.  But if so many places be found in which there were both parties, that an equal division is impossible, as for example, if they are unequal in number, after those places have been distributed which have an equal number, the place that remains over shall be disposed of as is provided above in the case where there is but one place to be treated.

Notes.

Ancient Epitome of Canon CXVIII.

Those who have been converted from Donatus, let them divide the dioceses; and let the senior bishop make the division, and the junior choose which he will.

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