Here's a pic http://www.led-zeppelin.org/images/gear/becvar8_02.png
"What was the first track he used it on in the studio? "I'd gone to Alembic and there was someone working for them who had an offshoot company called Becvar. He had this eight-string bass in Californian Gothic with palm trees, a mandala and other stuff. It sounded fantastic, like a big harpsichord/piano thing. And so when Page came out with the first riff of Achilles he said, 'What are we going to do with the rest of it?'' I said '8 string bass!' It fit perfectly," John Paul Jones said to Rikki Rooksby in a September 1999 Bassist Magazine interview.
Jones eventually settled on "a sort of sub-Alembic 8-string, which was actually a Becvar. It was built by a guy who was at Alembic and then left the company to start on his own. It's just an amazing creature--sort of Gothic Revival in style. Actually, it's more California Gothic, with a mandala on the back, with little mermaids, sea shells and palm trees inlaid. A very fine instrument. Very loud. The Riff King it was called. When Page first heard it, he said, 'Oh, no. I'm not playing to that!'" John Paul Jones said in a Guitar World interview."
...from here... http://www.led-zeppelin.org/studio-and-live-gear/860