GIGANTIC LAND-LIZARD FROM AUSTRALIA. 
549 
the same general form and direction, but sloping a little more outwards, so that their 
inner or medial surfaces meet along the upper mid-line of the supporting ring at a 
more open angle (Plate 64, a', a). The antero-posterior diameter of the base of each 
core is 4\ inches, and is coextensive with that dimension of the supporting girdle : the 
transverse basal diameter of each upper core is the same : the height or length of the 
core taken along the upper medial line is 5^ inches ; taken along the outer side of the 
cone it is 4^ inches. 
Of the lateral horn-cores (&', b') the fore-and-aft length of the base is co-extensive 
with that of its supporting ring: the height of the core from the upper border of the 
base is 2 inches. The apex is less obtuse than that of the antecedent lateral core. 
The under side or basal border of the core b' is directly continued into the under 
and outer surface of the girdle. The outside vertical diameter of the antepenulti¬ 
mate girdle is 6-g- inches, its transverse diameter taken at the interspace of the dorsal 
and lateral cores is 7 inches. The same diameter of the area of the girdle is 5 inches ; 
its vertical diameter is 4\ inches. The contour of the anterior outlet is subquadrate 
with the angles broadly rounded off, and the sides bulging a little inward opposite 
the caudal diapophyses. 
The penultimate segment presents a similar structure to the preceding, with some 
loss of depth and breadth, and a little increase of length, viewed laterally, as in 
Plate 65, fig. 1. The homologous processes, or horn-cores, are indicated by the letters 
a" and b" in figures 1-3 of that Plate. The apex of a" is directed backward and 
outward, that of b" is relatively less produced than in the antecedent segment. 
The terminal segment (ib. ib., c) is a simple cone, with a base of 3 inches in both 
transverse and vertical diameters, and a subobtuse apex directed backward. 
At the under surface of the preserved parts of the tail-sheath (ib., fig. 3) the last 
two segments have the line of confluence more feebly marked than above or at the 
sides, their respective contributions to the under surface being indicated by a shallow 
linear transverse depression. The under surface of the antepenultimate segment 
(ib., &*) is broadly heptagonal, with the anterior transverse border forming a low angle 
forward. The corresponding part of the free segment is, in great part, broken away. 
The whole of the preserved under surface of the above portion of the tail-sheath is 
flattened and shows marks of attrition against the surface on which the Megalama 
trod, as if ossification had there extended into the dermal coat. 
That the horny sheaths of the above-described bony supports or cores arming the 
end of the tail may have been applied to deliver blows upon an assailant, seems not 
improbable, and this part of the organisation of the great extinct Australian Dragon 
may be regarded, with the cranial horns, as parts of both an offensive and defensive 
apparatus. 
As with the cranial weapons, so with the caudal ones, examination and comparison 
were, in the first place, instituted in relation to all available specimens of existing 
Lacertilia; and the most notable instance of tail-armature seemed to be that of a small 
4 B 2 
