They are supposed by Professor Owen to be the trails of more than one species of articulate animal, probably allied to the King Crab, or limulus.
"The Student's Elements of Geology"
Sir Charles Lyell
A sample of foul-smelling limulus blood full of bacteria will become colorless on standing in a test tube for 10 to 15 minutes, but the blue color quickly returns if shaken with air.
"The Nature of Animal Light"
E. Newton Harvey
One is the limulus or "king-crab," which seems to be a descendant, or near relative, of the Trilobite, and has survived until modern times.
"The Story of Evolution"
Joseph McCabe