PRECAUD A L VERTEBRA OF ICHTHYOSAURUS AUSTRALIS — ETHERIDGE. 67 
outwards, thus rendering the longitudinal or lateral surfaces of the 
centrum somewhat concave. The depth of the concavities is an 
inch, or perhaps a little more, and a longitudinal section of the 
centrum would be, in consequence, of a strongly hour-glass shaped 
outline. The floor of the myelonal canal is three-quarters of an 
inch wide, the joint faces of the neurapophysial surfaces rather 
triangular on very strongly raised fore and aft synchondrosial 
articular elevations, the space between these and the diapophysial 
tubercles is roughly three inches, the latter having descended in 
close contiguity to the parapophysial tubercles. It is clear, there- 
fore, that this vertebra from the wide disassociation of the neura- 
and diapophyses occupied a position in the column certainly more 
than one-third of the trunk from the head, and, according to 
Owen’s measurements, was near about the forty to forty-fifth 
vertebra, for in this region in Ichthyosaurus, the dia- and para- 
pophyses form a pair of separate tubercles on each side near the 
anterior end of the centrum. 
The diapophyses are set further in from the anterior articular 
edge than the parapophyses ; these are close to the latter, but are 
not connected with it by a “neck.” Both are represented by 
large and strong rounded tubercles, separated from one another 
by an interval of two-eighths of an inch, this interstitial surface 
being deep and groove- like. The hremal surface is quite plain. 
The posterior concave articular surface is infilled with matrix, 
affording a complete cast of the next succeeding anterior cup, and 
even retaining a portion of the osseous tissue of the latter adhering 
to it. This tissue throughout the centrum is well preserved and 
dense. 
The specimen is certainly of the Campylodont group of Ichthyo- 
sauri, and occupies an intermediate position in outline between 
an “early posterior dorsal” and a “late posterior dorsal” vertebra 
of I . triyonus, Owen.* 
The largest Ichthyosauri attained a length of from thirty to 
forty feet, and the present meridianal species was in no way 
inferior to its gigantic fellows of the European Secondary seas. 
If we apply a similar method of arriving at the comparative size 
of an Ichthyosaurus as that adopted by Prof. Owen, that the 
jaw was “ thirteen times the length of the vertical diameter of 
an abdominal or anterior caudal centrum,” we see in the present 
fossil the representative of an animal possessing a jaw a little 
over five feet in length — thus 13 x 5" = 65" = 5' 5" long. Prof. 
McCoy computedf the remains of his type specimen to represent 
* Lydekker — Brit. Mus. Cat. Foss. Reptilia and Amphibia, 1889, pt. 2, 
p. 26, figs. 13 and 14. 
f Trans. Roy, Soc, Viet , ix., 2, 1869, p. 77. 
