All trilobites known from the Ardwell Group, Craighead Inlier, Girvan district are listed and frequencies recorded. Encrinuroides lapworthi n. sp. from the Sericoidea Mudstones, and Bumastoides fornax n. sp. from the Kiln Mudstones, are described. The Sericoidea Mudstones constitute a deeper water interlude in the complex succession which comprises the Craighead Limestone Formation; graptolites from this horizon indicate low Dicranograptus clingani zone. The closest resemblance of the trilobite assemblage as a whole is to faunas of Trenton age in North America. The occurrence of forms allied to Boda Limestone (Ashgill) species suggests that these are long-ranging, carbonate associated, trilobite stocks.
