Diagnosis.—Caulostrepsis with a vane, characterized by the possession of several commonly overlapping grooves branched out from the aperture, forming a fan-like structure. The grooves are generally longer than the tripled width of the boring.

Remarks.—Similarly to the other described ichnospecies of Caulostrepsis, it is interpreted that C. penicillus isp. nov. was originally a subsurface gallery, whose roof was eroded or collapsed. It is most similar to C. avipes, but its grooves branch out from the aperture, and they are much more numerous and distinctly longer. The grooves were probably produced by the tentacles of spionid, cirratulid, or similar bioeroding polychaetes, but the tracemaker presumably had them much more than the tracemaker of C. avipes. There were no transitions between C. penicillus isp. nov. and C. avipes observed in the material studied