We haven’t been able to identify the coat of arms in this bookplate. It is found in our copy of Bernardino Campelli’s Delle historie di Spoleti : sopplimento di quelle del regno d’Italia nella parte, che tocca al ducato Spoletino, à principi di esso, & alla città, che ne fù capo (Spoleto: Giovanni Domenico Ricci, 1672). Since this is a history of Spoleto, I thought the arms might be associated with that city, but the Spoleto arms are quite different. All I know for sure is that the arms belong to someone who is both a prelate (because of the ecclesiastical hat with tassels) and a member of the nobility. The crown looks–to me–like that of a marquess, but this is heraldry and I could be very, very wrong.
(In fact, the only thing I’m ever certain about when it comes to heraldry is that, after hours of research, I will know less about the subject than I did before. I will spare you the sad tale of when I thought the cap of maintenance was an old ducal hat–except to say that English monarchs would have been shocked by the suddenly very large number of dukes rattling about the country.)
If you can identify these arms please leave a comment here or on our Flickr provenance identification site (where the image is much sharper).