Nepeid trilobites of the Middle Cambrian of northern Australia

Twenty-five species of the Middle Cambrian Nepeidae of northern Australia are described; of these 10 are presented in open nomenclature, and 14 are named new. Four genera are recognized: Nepea Whitehouse and three new-Penarosa, Loxonepea, and FoIliceps. Of these Loxonepea is reminiscent of some Menomoniidae. The stratigraphic distribution is uneven; Nepea dominates in the Zone of Ptychagnostus nathorsti and Penarosa in the earlier zones. It is, however, apparent that they represent concurrent stocks. The older form to appear belongs to the Nepea stock. The currently used Middle Cambrian scale is essentially the Scandinavian agnostid scale of zones; the name Hypagnostus parvifrons Zone is, however, replaced by the name ElIagnostlls opimlls Zone. Collecting sites are described in superpositional order of strata. It appears that the nepeids lived in swarms floating most of the time in the surface waters. as inferred from the mode of embedding, from the occurrence in all kinds of sediments, the thin test, and the frontal boss-presumably a device to facilitate floating.