Following up on Kevin's last post:
He has already shared a good deal of his expertise, and his collection 
of Twainiana, for an e-essay on Mark Twain Collectibles on my Mark Twain 
In His Times site.  You can find it at 
"http://etext.lib.virginia.edu/railton/sc_as_mt/merchandiz/macdonnell.html"   
Steve Railton