bilobites

from The Century Dictionary.

• noun A name given by Linnæus, in 1775, to a genus of fossil brachiopods, of small size, in which both valves are strongly bilobed by a median sinus.
• noun A name given by post-Linnean authors to certain lobed (usually bilobed) markings, in the older Paleozoic rocks, which have been variously regarded as fossil fucoids, the casts of impressions produced by worms, crustaceans, and jellyfishes, and also as of purely mechanical origin.