A new ichnospecies, Gunnellichnus bartelsi is described on osteic substrates. These tracesresulted from the activities of an infection that penetrated through the epidermal scutes onthe external surface of turtle carapace and plastron bone. Gunnellichnus bartelsi appears tooccur solely, or at least dominantly, on the dermatemydid turtle Baptemys wyomingensis. andonly on the carapace of these taxa. Gunnellichnus bartelsi are identical to lesions attributedCarapacial Shell Disease (CSD) on kinosternid turtles, which was shown to be caused bycolonization by filamentous algae. Like all Gunnellichnus ichnospecies, G. bartelsi is interpretedto record an infection on unhealthy host organisms, or those that live in stressed environmentalsettings.