The Collaborative International Dictionary of English v.0.48:

Scolithus \Scol"i*thus\ (? or ?), n. [NL., fr. Gr. skw`lhx a
   worm + li`qos a stone.] (Paleon.)
   A tubular structure found in Potsdam sandstone, and believed
   to be the fossil burrow of a marine worm.
   [1913 Webster]