Small reptiles from the Early Jurassic Pant 4 fissure fill in Glamorgan, South Wales (St. Bride’s Island, Pant Quarry), were formerly provisionally attributed to three spe- cies of sphenodontian lepidosaurs. A re-analysis, aided by new material, has found this herpeto-fauna to consist almost exclu- sively of a single new species, Clevosaurus convallis sp. nov., with only one specimen referable to Sphenodontia incertae sedis. Clevosaurus is known from the Upper Triassic and Lower Jurassic in various parts of the world, but C. convallis represents the first occurrence of the genus in the Jurassic of Britain. The material is fragmentary but includes numerous premaxillae, maxillae, dentaries and palatines, and the new species is distinguished by the unique combination of six large additional dentary teeth and a very short nasal process of the premaxilla, along with the diagnostic Clevosaurus features.