Please note that Mommsen uses the AUC chronology (Ab Urbe Condita), i.e. from the founding of the City of Rome. You can use this reference table to have the B.C. dates
From: The History of Rome, by Theodor Mommsen
Translated with the sanction of the author by William Purdie Dickson
Election of Priests by the Community
Along with this change the formal powers of the people in the nomination of magistrates as well as in questions of government, administration, and finance, received a hazardous extension. The priesthoods--particularly those politically most important, the colleges of men of lore--according to ancient custom filled up the vacancies in their own ranks, and nominated also their own presidents, where these corporations had presidents at all; and in fact, for such institutions destined to transmit the knowledge of divine things from generation to generation, the only form of election in keeping with their spirit was cooptation.
It was therefore--although not of great political importance--significant of the incipient disorganization of the republican arrangements, that at this time (before 542), while election into the colleges themselves was left on its former footing, the designation of the presidents--the -curiones- and -pontifices- --from the ranks of those corporations was transferred from the colleges to the community. In this case, however, with a pious regard for forms that is genuinely Roman, in order to avoid any error, only a minority of the tribes, and therefore not the "people," completed the act of election.
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Reference address : http://www.ellopos.net/elpenor/rome/3-11-government-governed.asp?pg=78