Fig. 3. Mandibular pars molaris in Cambrian and extant Tetraconata. (A–D) Early Cambrian crustacean from the Mount Cap biota, northwestern Canada. Images courtesy of T. H. J. Harvey and N. J. Butterfield. (A) Light micrographs, scale 100 mm. (B–D) Scanning electron micrographs; scale in B applies to C–D. (B) scale 50 mm. (C) Marginal setal fringe, outer margin to right, scale 6 mm. (D) Transition between marginal fringe (at right) and rows on branching spines on molar surface; scale 8 mm. (E) Cyclestheria hislopi (Branchiopoda: Cyclestherida), scale 10 mm. (F) Nesomachilis howensis (Insecta: Archaeognatha), scale 30 mm. (G) Meganictyphanes norvegica (Malacostraca: Euphausiacea), scale 10 mm. Images E and G courtesy of S. Richter.