|Canterbury Cathedral choir|
It looks to me as though there are actually two monsters or creatures or whatever they are in this story. I think that might be new for an MRJ story--both his ghosts and his scholars are usually loner types. We have one imprisoned under the pulpit, and once the pulpit is gone, it starts waking up and struggling to get out. Meanwhile its mate, or its friend, is running around the cathedral close every night, scaring everyone out of their wits, and it would probably be a bad idea to leave any animals unsecured out there. But once the bound monster escapes (and it, naturally, is "all over hair"), they are never heard of again.
The inscription, "Ibi cubavit Lamia," is from the Vulgate Bible. I have two quite different translations of the phrase here. The KJV renders it as "There hath the lamia lain down and found rest for itself." Rosemary Pardoe shows it as "There shall be the lair of the night monster."
And Rosemary Pardoe has quite an interesting short article about an apparent hoax based on this story! Head over to the Ghosts and Scholars archive and read "The Demon in the Cathedral."