What is the name given to a census of the Senatorial or decurional rolls conducted by a Roman magistrate?

The correct choice is "Censio," which refers to the process of conducting a census to update and maintain the rolls of citizens, including the Senatorial or decurional ranks. In ancient Rome, this procedure was essential for various administrative purposes, such as taxation and military service. The magistrate responsible for carrying out the census would assess and record the names and statuses of citizens, which helped maintain the organization and governance of the Roman state.

Other terms listed primarily refer to different administrative or registration processes. "Lectio" relates to the reading or selection of names or candidates, "Registratio" involves the act of registering without the specific context of census-taking, and "Enumeratio" generally means enumeration but does not specifically pertain to the census of decurions or senators. Therefore, "Censio" is the most accurate answer in this context.