The fossil, thought to be 150 million years old, was found when a rock was cracked open, revealing the one-inch-long black ink sac.
A picture of the creature and its Latin name was drawn using its ink.
Dr Phil Wilby of the British Geological Survey said it was an ancient creature similar to the modern-day squid.
"The structure is similar to ink from a modern squid so we can write with it," he said. 'Medusa effect'
The find was made at a site which was first excavated in Victorian times where thousands of Jurassic fossils with preserved soft tissues were found.
Dr Wilby, who led the excavation, said: "We think that these creatures were swimming around during the Jurassic period and were turned to stone soon after death. It's called the Medusa effect."