66 KECORDS OF THE AUSTRALIAN MUSEUM. 



On a PRECAUDAL VERTEBRA op ICHTHYOSAURUS 

 AUSTRAL IS, 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 vertebrse, 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 /. 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 pleui'apophyses, but having the articular 

 surfaces of the first and last well displayed. The positions of the 

 diapophy.sial 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 

 hfemal 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 

 V)etween the dia- and pleuraphysial tubercles the centrum is 

 exactly two inches, but on the hajmal 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 

 l)etween the vertelDn-e, 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. Vict., viii., 1868, p. 41. 



t Owen — Mon. Foss. Reptilia Cret. Formation, p. 70, pi. xxii. 



