FOSSIL VARANIDAE AND MEGALANIDAE. 
437 
stress ought, to my mind, be laid on the fact, not always sufficiently pointed 
out heretofore by literature amongst the characters distinguishing Mosa- 
sauria, residing in an ossified sclerotical ring common to numerous 
Mosasauria and never met with in the Platynota group. (Textfig. 
25). It were furthermore of importance to ascertain the presence of teeth 
on the pterygoid of Aigialosauridae, as supposed by Nopcsa 1 , for, in this 
case, the palate’s dentition could not by far be considered as variable, 
inconstant a character, as for instance with some recent Lacertae. 2 Refe- 
rence has been made to these 
two characteristics, as experi¬ 
ence has proved that they have 
not been taken into due con¬ 
sideration with regard to phy- 
letical connexions. The struc¬ 
ture of the vertebrae present 
differences of yet greater bea¬ 
ring (Tex fig. 26), which natu¬ 
rally culminate in the mor¬ 
phology of the extremities and 
sus pensorialgirdles (see Textfig. 
27). To enter into these details 
were too great a digression from 
our subject with regard to which 
I can only refer the reader to 
Osborn’s already mentioned val¬ 
uable work. Bo much however 
may undoubtedly be stated 
that the differences between the Platynota and Mosasauria exact a most 
careful examination, and although physiological phenomena hinder me to 
a certain degree in accepting in every case a slow course of evolution, 
relatively sudden transformations of so high a degree reaching such a far 
extended Reptilian group, as required by either Boulenger’s or Nopcsa ’s 
theory, appears to me at best as not being up to now sufficiently proved. 
If however we should search for conciliating motives, Baur’s theory 
might offer a compromise, as deriving Mosasauria «from unguiculate 
Lacertilia» «which were very close to the Varanidae» — and considering 
certain very heteregeneous families of the modern system — our good 
1 Geol. Mag., op. cit. p. 120, footnote 1 . 
2 See for this purpose : Méhely, Mater, z. einer Syst. u. Phyl. d. muralis ähnlichen 
Lacerten, Ann. Mus. Nat. Hung., Voi. VII, Budapest. 1909. 
Fig. 26. Cervical vertebra of f Clidastes stenops 
Cope laterally and anteriorly viewed. — From 
Cope (in Broili, op. cit. Fig. 351.) 
