Opisthias is a genus of sphenodont reptile. The type species, Opisthias rarus, is known from the Late Jurassic Morrison Formation of western North America, present in stratigraphic zones 2 and 4–6. A lower jaw is also known from the Berriasian aged Lulworth Formation of the United Kingdom, which appears to be distinct from the type North American species. Other remains are also known from the Late Jurassic of Portugal.