I have the same Thayer black velvet web back that you have. The black art
slit is where you place the card; thread it from the rear.
It appears somewhere along the line that the Thayer (also, Owen still makes
one with a nearly identical web; see their latest catalog) web has been
placed on a metal base; hence you have a bastardized prop. I can't tell from
the picture whether you have an original Thayer or Owen wood spider that
someone has painted silver (it should be painted red/black/yellow) or, if in
fact, you have a pewter or silver painted metal spider ( however, I never
heard of anyone making the spider out of metal). Also, Abbott's made one. In
addition, I believe Hank Lee and Daytona, Magic (Florida) sell a new one made
today. I don't know the price of the new one - but suspect you could purchase
a new one or find any of the others at used magic auctions/dealers for less
than $250 - unless, of course, this one is actually some early 1900's metal
European made one - although I have never heard of this effect as such a
collectible.

Best regards,
Gale