[Illustration: Fig. 3. Occipital region of skulls of _Megalocephalus
brevicornis_ (x 3/10, after Watson, 1926, as _Orthosaurus_),
_Dvinosaurus_ (x 1/4, modified after Bystrow, 1938; the lower figure
after Sushkin, 1936), and _Necturus maculosus_ (x 3, original, from K.
U., No. 3471).