Trilobites with appendages from the Middle Cambrian, Burgess Shale, British Columbia

New and old material of Olenoides serratus is described. Hypostome was fused with rostral plate, presence of metastome uncertain. Uniramous, multijointed antenna and posterior cercus were each of length three-quarters that of exoskeleton. Individuals of different sizes show 14-16 pairs of biramous appendages. Coxa was large, strongly spinose on ventral and adaxial margins. Inner, leg branch of 6 segments and terminal spines, long spines on proximal podomeres on ventral side. Outer branch arose from dorso-posterior margin of coxa, bilobed, inner lobe bearing some 50 slim filaments which extended back over two following appendages. All speeimens show appendages displaced, reconstruction suggests only 3 biramous pairs on cephalon, 7 on thorax, and 4 to 6 on pygidium. Speeies considered a predator and scavenger, food grasped by spinose leg branches, squeezed by gnathobases and passed forward in midline. Outer branches considered a gill, probably also used in swimming. Gait, trackway, and manner of digging and raking are suggested. No new material of Kootenia burgessensis found, Walcott's single specimen shows no clear evidence of anterior rim of shaft of gill branch.