New Species of the Brachiopod Cyrtina from the Middle Devonian Hamilton Strata of Southwestern Ontario

Brachiopods from the Middle Devonian strata of southwestern Ontario a re removed from the over-extended species Cyrtina hamiltonensis (Hall), which i s basedupon specimens from New York state. They a re assigned to four new species of Cyrtina. C. angularis, the largest (attaining over 20 mm in width), is from the Widder Formation, wherein it occurs abundantly in Unit 11 (the "Cyrtina bedw at the Widder locality); it is characterized by a deep subangular sulcus with a median depression and a fold with a t most only a shallow depression. C. s d h w m t h i , a small species from the lower part of Unit 14 of the Widder Formation, has very fine spinules on i ts surface and no median depression in either the fold o r the lowandbroad sulcus. C. cou l t i smm, a small Cyvtina from the Hungry Hollow Formation, differs from C. sozlthwmthi in having a prominent highfold, conspicuous growthlamellae, andcoarse spinules. C. arkonensis, amedium-size species from theArkona Shale at various localities, i s distinguished from C. angularis by its shallow rounded sulcus and more numerous costae. The four species of this brachiopod genus are so distinctive that they can readily be used in stratigraphic work.