A &IGANTIC LAND-LIZAED FEOM AUSTEALIA. 
47 
of Meqalania is the sole representative of the neural spine : in Hydrosaurus giganteus 
the ridge rises to the proportions of a spinous process. But, apart from these generic 
or subgeneric differences, the correspondence is complete betv^een the extinct and above- 
cited existing Monitor-lizards of Australia. 
The three or four vertebrae at the base of the neck, supporting free ribs, in Hydro- 
sauTUS, exhibit the same modification of the costal tubercle as in the second vertebra of 
Megalania (Plate VIII. fig. 1, d) : those vertebrae, also, show the median tract defined by 
the two side-grooves on the under surface. The vertebrae in advance of these, in Hy- 
drosaurus, have the median tract produced into a hypapophysis. 
Vertebrae of HLegalania will probably be discovered showing this character ; and, 
indeed, from the correspondences already determined, it may be inferred that the same 
local modifications of the vertebral column prevailed in the bony structure oi Megalania 
as in that of the existing Australian Monitors. 
Among these land-lizards, it is interesting to find that one species, which attains the 
length of upwards of 6 feet, has been dignified with the specific name of giganteus, on 
account of this unusually large size compared with the generality of existing Lacertilia. 
Whether among the vast and unexplored wildernesses of the Australian continent any 
living representative of the more truly gigantic Megalania still lingers, may be a ques- 
tion worth the attention of travellers. But, most probably, like the gigantic Marsupials, 
Biprotodon and Nototherium, with whose fossil remains those of Megalania were asso- 
ciated in the tertiary deposits now cut through by the Condamine and its tributaries, 
the gigantic land-lizard has long been extinct. 
The proccelian type of vertebra, or that in which the articular cup is in front and the 
ball behind, characteristic of the fossils above described, was first introduced in the 
Reptihan class, according to present knowledge, during the liassic period; but, from 
that to the upper oolite, it was manifested only by Pterodactyles. The earliest exam- 
ples of proccelian vertebrae in Lacertian reptiles date from the W ealden period ; in Croco- 
dilian reptiles the proccelian type first appears at the cretaceous period *. 
The o nl y known proccelian lizards comparable in size with the large Australian one, 
represented by the three above-described vertebrae, are the Mosasaurus and Leiodon of 
the Greensand and Chalk strata. 
The inferior depth of the cup and production of the ball, the vertical position of both 
at right angles with the axis of the centrum, and many minor modifications of the ver- 
tebrae of those large Lacertians of the cretaceous period, show great differences between 
them and the fossil proccelian vertebrae of the freshwater tertiary deposits of Australia. 
The Mosasauroids were, in fact, a family of marine lizards so distinct from existing spe- 
cies, as to form the type of a suborder. 
The fossil remains of European proccelian lizards, which, like the large vertebrae under 
* In the Greensand of New Jersey, North America (Proceedings of the Geological Society, January 31, 
1849) ; iu the Upper Greensand near Cambridge, England ; in the ‘ Calcaire pisolithique ’ of Mont Aime, 
Departement de la Marne ; and in the upper cretaceous stone at Maestricht. 
