Adam Clarke on Acts 13:21

Saul the son of Cis - In all proper names quoted from the Old Testament, we should undoubtedly follow, as nearly as possible, the same orthography: קיש Kish, was the name of this king's father, and so we spell it in the Old Testament, and yet have transformed it into Cis in the New, where the orthography is almost entirely lost.

The space of forty years - Reckoning from the time of his anointing by Samuel to the time of his death, from a.m. 2909 to 2949.