Diagnosis: A central, rounded depression surrounded by a flat shelf lightly etched into the substrate. The shelf has a subcircular to oval, crenulated perimeter, and may be patterned with concentric rings having the same crenulations (Bromley and Martinell, 1991).

Description: Concave traces consisting of a central depression of circular to oval shape. A shallow shelf, created by several weakly developed crenulated rings, is present around the depression’s perimeter. Cordedlamellae are also visible in the inner central depression on the best developed specimen. Trace diameter ranges from 2.2 to 6.3 mm. on the host shell’s surface, suggesting the possible identity of the trace-makers.

Remarks: Centrichnus concentricus is very similar to Sedilichnus halo Neumann and Wisshak (2009), and it isnecessary to clearly fix the differences to prevent confusion of these two ichnotaxa. The difference lies in the type of tracemaker and ethological interpretation. C. concentricus represents an etching trace, i.e., fixichnia sensu de Gibert et al. (2004).

Diagnosis: (After Bromley & Martinell 1991, p. 247.) “Tear- or drop-shaped Centrichnus comprising a series of bundled or crowded, bow-shaped grooves concave toward the pointed end.”