Skolithos linearis (Haldeman, 1840)

Redefined diagnosis (herein). Vertical to slightly inclined, cylindrical to sub-cylindrical, straight to slightly curved, unbranched burrow, more or less distinctly lined, with homogeneous fill and very high length-to-diameter ratio.

Emended diagnosis: Cylindrical to subcylindrical, perfectly straight and vertical to slightly curved or inclined burrows. Burrow wall distinct to indistinct, may be annulated.

Discussion: Skolithos is generally interpreted as the domichnion of a suspension-feeding worm or phoronid (summarized in Fürsich 1974b). However, the possibility that certain Skolithos represent entrance shafts to more complicated burrows cannot be excluded (BUCKMAN 1996). The occurrence of a wall lining or lack thereof may be explained as a reaction of the burrower to differences in sediment cohesiveness, as a wall gives the burrow more stability.

Diagnosis. burrows cylindrical to subcylindrical, perfectly straught and vertical to slightly curved or inclined. up to a meter in lenght. Diameter 3 to 7 mm, commonly repoeted up to 12mm. Burrow wsll distinct to indistinct.

Diagnosis Cylindrical to slightly subcylindrical, straight to curved, distinctly walled, rarely branched, vertical to steeply inclined burrows. Classification Preserved as endichnia. Interpreted as dwelling structures of vermiform animals.

Description. Burrows are unrnamented, simple, straight to slightly sinuous structures typically 3 -6mm in diameter and as much as 1 m in maximum length. Locally, burrow length is controlled by bed thickness. Rare specimens of a much larger form of S. linearis occur locally, but these structures, as much as 2 cm in diameter, seem to be relatively unimportant components of prevalent ichnofacies.