Coelostegus prothales (Carroll and Baird 1972) lived ~310 mya and was a little larger than its predecessor Paleothyris and its sister, Hylonomus. Both preceded Protorothyris.
In the skull the frontals have posterior processes. Here the supratemporals are angled down and the cervicals are slightly larger than the dorsals.
The vertebrae and ribs were much more robust. They were taller than long and the neural spines were taller than each centrum. There were fewer than 31 presacral vertebrae.
The scapulocoracoid was not well ossified. The limbs and tail are unknown.