This subgenus is founded on four skulls, forming part of the collection transmitted to the British Museum in 1858, by His Excellency Governor Sir George Grey, K.C.B., from the sandstone rocks at the foot of the Rhenosterberg, S. Africa. These skulls belong, by their dentition, to the Dicynodont family, but present such strongly marked deviations from the type species of the genus (Dicynodon lacerticeps, Ow.) as to indicate a distinct subgeneric section; they were accordingly entered in the Museum list, and labelled in the cabinet where they are exposed to view, under the term Ptychognathus.