66 
RECORDS OF THE AUSTRALIAN MUSEUM. 
On a PRECAUDAL VERTEBRA of ICHTHYOSAURUS 
AUSTRALIS , McCOY. 
By R. Etheridge, Junr., Curator. 
The subject of this paper is the imperfect vertebra of a large 
Ichthyopterigian, referable, I believe, to Ichthyosaurus australis , 
McCoy.* The original was brought under my notice by the Rev. 
M. Kirkpatrick, of Bega, N. S. Wales, who obtained it from 
Marathon, Central Queensland. With his permission a cast was 
taken for the Australian Museum Collection, As Sir F. McCoy’s 
description was very brief, an extended notice of one of the middle 
trunk, or anterior pre-caudal vertebrae, may be acceptable to Aus- 
tralian investigators. 
The specimen is the centrum of a large vertebra measuring five 
inches in its vertical and transverse diameters, and rivals in size 
those of the gigantic I. campylodon , Carter, from the European 
Chalk, the vertebra figuredf by the late Sir Richard Owen measur- 
ing only four inches high. Our example is devoid of the neural 
spine, neurapophyses, and pleurapophyses, but having the articular 
surfaces of the first and last well displayed. The positions of the 
diapophysial and pleurapophysial articular surfaces leads to the 
belief that the vertebra is one of the middle trunk series. It is 
subcircular in outline, slightly narrowed and contracted neurally. 
Measured across the articular surfaces from the neural to the 
haemal margins the diameter is exactly five inches, and in a trans- 
verse direction, from diapophysis to diapophysis it is an eighth of 
an inch short of a similar measurement. Longitudinally measured 
between the dia- and pleuraphysial tubercles the centrum is 
exactly two inches, but on the hsemal surface it is a quarter of 
an inch more. 
The concave terminal articular surface visible is deep, terminat- 
ing in a central fossa, the extent of the concavity being well 
exemplified by the matrix cast of the anterior cavity of the 
succeeding vertebra? at the posterior end of this specimen. This 
mass of matrix represents the “ elastic capsule ” that intervened 
between the vertebra?, and retains on its surface portions of the 
osseous tissue of the succeeding centrum. The periphery or im- 
mediate articular rim at each end is narrow, the surface thence 
sloping rapidly inwards, but the edges of the rims project slightly 
* Trans. Roy. Soc. Viet., viii., 1868, p. 41. 
f Owen — Mon. Foss. Reptilia Cret. Formation, p. 79, pi. xxii. 
