Numbers 26:50

The families of Naphtali— Reckoning the tribes twelve, exclusive of the tribe of Levi, (which was not to be settled as a tribe,) there will be twelve tribes and fifty-eight families in all, which make seventy; whence some conjecture, that the number of seventy elders was taken from the number of princes of tribes and heads of families. The princes of tribes led each tribe, and had the administration of their public affairs. The office of the heads of families was to assemble the families of which they were governors. They may be represented as lords lieutenant of counties and their deputy-lieutenants, or as generals and lieutenant-generals. See Lowman's Dissert. p. 76.