What is "coelognathus"

Coelognathus is a genus of five ratsnakes that were formerly assigned to the genus Elaphe. Based on morphological evidence and protein similarities, in 2001 Helfenberger re-validated the name Coelognathus that had originally been proposed by Leopold Fitzinger in 1843. The distinction between Coelognathus and Elaphe was further supported by mitochondrial DNA sequence and additional morphological evidence in 2005.