Diplocraterion parallelum Torell, 1870

Emended diagnosis: Vertical Diplocraterion with parallel limbs and a width/length ratio below 0.5.

Emended diagnosis: Vertical, U-shaped, single-spreite burrows; spreite may be unidirectional or bidirectional, generally continuous, rarely discontinuous. Limbs unlined and smooth, or with bioglyphs (longitudinal or transverse ridges and grooves). Limbs either parallel, or diverging upward or downward; top of limbs sometimes with funnel shaped opening.

Discussion.--Following the proposition of Fürsich (1974), the observed burrows must be referred to D. parallelum and the trace probably corresponds to a dwelling burrow of a suspension-feeding animal, possibly a small crustacean. D. parallelum is very abundant in sandy beds showing ripple marks on their upper surface. Here, the trace appears as a typical dumbbell-shaped convex epirelief showing a preferential orientation to the current (Fig. 10). This observation supports the suspension-feeding hypothesis.

Description: Vertical U-shaped burrows preserved in full relief with concave-upward spreiten; spreiten is enhanced by lining of the walls; limbs of burrow walls are parallel. Both retrusive and protrusive forms occur and few specimens display both forms; bottom of burrows are semicircular or more rarely flattened; burrows are 8-25 mm in tube diameter and 25-180 mm in distance between limbs; depth of burrows is 25-510 mm; smaller specimens occur in large numbers in distinct horizons, while larger specimens mostly occur solitarily.