507 
■would probably present a deeply sigmoidal outline if whole. It now measures through 
the base of the alveolus an inch and one-eighth, the latter being six-eighths of an inch 
deep. From the bottom of the alveolus through the inner portion of the dentary there 
is only a thickness of three-sixteenths of an inch. The upper element of this bone is 
nearly as correspondingly thick as the lower portion of the pre-maxillary, whilst that 
part below the alveolus, including the portion split off, is at least one inch in height. 
The external lougitudinal groove leads into a sac, which, with the passage uniting the 
latter to the outer groove, almost completely cuts the bone itself in half, and strongly 
resembles the similar vascular canal in the pre-maxillary. We also notice in this section 
the difference in the angle of the alveolus in tho upper and lower jaws, and doubtless 
the curved outline of the lower teeth is a provision of nature to bring them into 
apposition with those of tho upper jaw, which are straighter and set at an entirely 
different angle. 
I do not see any trace of the splouial bones, the fracture which severed this 
portion of the jaws from the remainder of the head having taken place too far forward, 
unless the small fragment of bone at the very bottom of the section in the middle 
line represents the anterior termination of the right splenial. 
Since Prof. Sir F. McCoy’s first announcement of Eualiosaurian remains in 
Queensland very little seems to have been done towards working out tho distribution of 
this important group of reptiles in Australia. The details of his Ichthi/osaurus australis 
given by McCoy are so meagre that it is with the greatest difficulty a comparison can 
be instituted with any other remains. The presence of the casts in the Australian 
Museum would have rendered this task easier than it otherwise could have been had 
that portion of tho head mentioned by McCoy as bearing teeth been present, but the 
cast in the Museum consists of a portion of the right side included between the 
posterior margin of the orbit to about half the length of the nostrils, measuring one 
foot in length by seven and a-half inches high. This portion of the cranium is, of 
Course, much posterior to that here described, but, judging from the relative pro- 
portions of the two specimens, I am inclined to regard the present fragment as a 
portion of a species quite as large as Sir F. McCoy’s, and it is possible they may be 
identical. 
The general proportions of this snout resemble those of J. campyloion, Carter, 
from the English Chalk, and there is present in this species a well-marked vascular 
channel * * * § along the pre-maxillary and dentary bones, just as vfQ see it here. Describing 
this. Sir Eiehard Owen says : “ Opposite the origin of the inner alveolar plate the pre- 
maxillary is traversed by a straight longitudinal groove, four lines in breadth, which 
contracts as it advances forwards. ”t Touching the similar groove seen along the 
dentary, he adds : “ The outer part of tho dentary at tho hinder fracture is six lines in 
thickness, smooth, and convex on its outer side, which is traversed by a longitudinal 
groove, which also slightly narrow's as it advances.” 
As W'ell as in I. campylodon, this groove is shown in Sir K. Owen’s figures of the 
jaw's of I. coimiunis J and I. platyodon,% Liassic species. 
Sir F. McCoy notes the resemblance of the teeth of his I. australis to those of 
I- campylodon, previously referred to, a likeness which is also perceptible in our species. 
I am unable, however, to institute a comparison between the latter and I. australis, 
from the fact that the casts in the Australian Museum do not exhibit the teeth. 
* Mon. Foss. Kept. Cret. Form., 1851, t. 25, fig. If/. 
t ioc. cit. , p. 75. 
t Mon. Foss. Kept. Lia.ssic Form., t. 21, f. 2. 
§ Ibid., t. 31, f. 2. 
