Abstract
Summary: Five trinucleid trilobites, belonging to the genera Onnia and Tretaspis, are described and figured from the higher beds of the Dufton Shales. Three are given new specific or subspecific names; the fourth is compared with Tretaspis ceriodes (Angelin), and the fifth, referred to an Irish form of similar age, is held to be a probable synonym of Tretaspis moeldenensis Cave, described originally from South Wales.

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