From the paper in which the Interrogatives were treated, by an inadvertency an was omitted. As there was every reason to expect, an is found to shorten a sub-joined hoc, id, etc.
Ad. 337 an ŏc proferendum tibi uidetur usquam? Ge. Mi quidem non placet. (So the vulg. since Bentley; but A has usquam esse, and the Calliopians have esse usquam. Room could be found for both words by a transposition, thus: an hŏc tibi uidetur proferendum esse usquam? etc.)