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
The plenitude of the consular power was further restricted in so far
as the administration of the military chest was committed to two
paymasters (-quaestores-) chosen by the community, who were nominated
for the first time in 307. The nomination as well of the two new
paymasters for war as of the two administering the city-chest now
passed over to the community; the consul retained merely the conduct
of the election instead of the election itself. The assembly in which
the paymasters were elected was that of the whole patricio-plebeian
freeholders, and voted by districts; an arrangement which likewise
involved a concession to the plebeian farmers, who had far more
command of these assemblies than of the centuriate -comitia-.
A concession of still greater consequence was that which allowed the
tribunes to share in the discussions of the senate. To admit the
tribunes to the hall where the senate sat, appeared to that body
beneath its dignity; so a bench was placed for them at the door that
they might from that spot follow its proceedings.