SUMMARY

Cochlichnus kochi is common in well-laminated mudstones in the Westphalian of the East Pennine Coalfield of Britain; 189 specimens were examined and 70 measured. This trace-fossil is a sinuous endichnial tunnel less than 1 mm diameter following a straightish repichnial path. Snake-like locomotion is reviewed and the geometry of C. kochi approximates to that of repeated clothoid curves, the transition curve of railway engineers. These curves allowed efficient propulsion through watery surface muds to an animal with a ‘hydrostatic skeleton’, probably a nematode.