This section is from the book "Popular Law Library Vol7 Equity Jurisprudence, Trusts, Equity Pleading", by Albert H. Putney. Also available from Amazon: Popular Law-Dictionary.
"A supplemental bill lies when there is a defect in the proceedings occurring too late to be remediable by amendment, or where, by an event subsequent to the commencement of the suit, a new interest in the matter in litigation is claimed by an existing party to the suit, or a new party claims, but not by mere operation of law, the interest which was claimed by an existing party. It is merely an addition to the original bill. It is a well settled rule that nothing can be inserted in an original bill by way of amendment, which has arisen subsequent to the commencement of the suit, but that the same must be stated in the supplemental bill. It may be filed to supply defects in the frame of the original bill, and this may be done either before or after decree, and to aid or impeach the decree, or to put new matter in issue, as a new interest vested in an old party, or an interest devolving upon a new party." 5
Where it is desired to bring in new parties as defendants to the bills, this must be done by a bill in the nature of a supplemental bill.6