OF A MEGALANIAN GENUS FROM LORD HOWE’S ISLAND. 
473 
channel (y) opening on the outer side of the “sella turcica”; with this opening 
communicates the “ trigeminal canal” (fig. 2, e). 
Returning to the base of this part of the skull, will be seen, half an inch from the 
mesial ends of the basi-sphenoidal ridges, a second basal floor formed by a flattened 
horizontal plate of bone with a smooth under-surface 2 inches broad at the hind border 
and narrowing as it advances to an inch and a quarter’s breadth, where it terminates 
with a forward production of its angles, between and above which protrudes a con¬ 
tinuation of the proper “ basis cranii ” constituting the floor of tire pituitary cavity. 
The interspace between the true and false basis cranii is 2 mm. vertically at the fore 
part, 3 mm. at the hind part of the supplementary plate. The breadth of the hinder 
interspace is 40 mm., of the anterior interspace 25 mm. The extreme breadth of this 
singularly complex part of the skull is 4 inches, the vertical diameter of the occiput 
is 3 inches ; but this would be exceeded if the superoccipital spine were entire. 
What I regard as the cranial outlet of the trigeminal nerve opens into a wider 
passage leading to the large irregular smooth-surfaced chamber (fig. I, x), excavated at 
the under part of the par-occipital production ( p ). The flatness of the basi-sphenoidal 
tract contrasts witli the concavity of that region shown at 5, fig. 2, Plate 36 (‘Phil. 
Trans.,’ 1880, vol. 171) in Megalama prisca. The amount and degree of modification 
of the hinder part of the skull of Meiolcinict add to other grounds for generic or sub¬ 
generic distinction of the present horned Saurian, manifested by the fossils next to be 
described. 
In the same block with the occipital part of the skull was sent the fore end of, 
apparently, the same skull (Plate 29, figs. 3-6), judging by relative size, colour, and 
state of fossilisation. This specimen included the floor of the outer nostril (figs. 3 and 
6, n, n) with a partial bony septum (ol) commencing half an inch behind the nasal 
aperture. The breadth of this nostril is llr inches; the smooth surface of the cavity 
to which it leads contrasts with the coarse reticulate sculpturing of the surface at the 
fore part of the upper jaw, which describes a transverse convex curve to the fractures 
(figs. 4, 6, m, m ), severing the fossil from the rest of the skull. The alveolar border 
(fig. 4) is a trenchant plate (a) with a semi-circular notch at the mid-line. The plate 
is thickened by a slight buttress of bone on each side of the notch ; there is not a 
trace of dental alveolus. The smooth channel (6), of which the trenchant border (a) 
forms the outer wall, is half an inch in breadth, and is bounded behind by a shorter 
and lower pair of ridges ( ib ., c, c) almost parallel with the foremost. Each of the 
hind ridges (c, c) commences opposite the thicker mesial part of the outer ridge (a). 
The intervening channel (d) sinks deeper than the lateral ones into the jaw’s 
substance. The bony palate extends backward from the mesial ends of the hind 
ridges, where it has a breadth of half an inch ; it narrows as it extends outwards to 
the terminations of those ridges. 
The floor of the nasal cavity (fig. 6, n) extends backward for half an inch behind the 
anterior opening, then abruptly sinks to a plane (fig. 5, g) half an inch below the hind 
MDCCCLXXXVI. 3 P 
