Fenestella
A Roman historian who, like Licinius Macer, held that the Roman year had twelve months from the start.
How the Romans fixed the year
Censorinus, On the Birthday 20–22 (238 CE), in the edition of Friedrich Hultsch (Leipzig, 1867) · 238 CE
de quibus omnibus disserere quoniam longum est, ad Romanorum annum transibimus. Annum vertentem Romae Licinius quidem Macer et postea Fenestella statim ab initio duodecim mensum fuisse scripserunt: sed magis Iunio Gracchano et Fulvio et Varroni et Suetonio aliisque credendum, qui decem mensum putarunt fuisse, ut tunc Albanis erat, unde orti Romani.
It would take too long to discuss all of these, so I will move on to the year of the Romans. Licinius Macer, and later Fenestella, wrote that the year at Rome had twelve months from the very beginning. But we should rather believe Junius Gracchanus, Fulvius, Varro, Suetonius and others, who thought it had ten months. So it was at that time among the Albans, from whom the Romans came.