STRUCTURE AND RELATIONSHIPS OF OPISTHOCELIAN DINOSAURS. 167 
confusion, at once annoying to the investigator and puzzling to the 
student. The oldest member of the group and the best known of the 
European genera is Cardiodon.* This was described by Owen in 1841, 
and for a long time included under the Crocodilia. 
The first recognition of the ordinal rank of the Cardiodont 
reptiles was offered by Owen in 1859, when he proposed for them the 
name Opisthoccelia, as one of three suborders of crocodiles. The 
group was characterized as follows:t **The small group of Crocodilia, 
so called, is an artificial one, based upon more or less of the anterior 
trunk vertebre being united by ball-and-socket joints, but having the 
ball in front instead of, as in modern crocodiles, behind. Cuvier first 
pointed out this peculiarity in a crocodilian from the Oxfordian beds 
at Honfleur and the Kimmeridgian at Havre. The Reporter has 
described similar opisthoccelian vertebre from the Great Odlite at 
Chipping Norton, from the Upper Lias of Whitby, and of much larger 
size, from the Wealden formations of Sussex and the Isle of Wight. 
These specimens probably belonged, as suggested by him in 1841 and 
1842, to the fore part of the same vertebral column as the vertebre, 
flat in the fore part and slightly hollow behind, on which he founded 
the genus Cefiosaurus.’’ 
In this classification Owen was followed by Haeckel, but Huxley, 
in the following year, included Cardiodon in the Iguanodontide. In 
1874 Seeley, describing the genus Craterosaurus, proposed for the 
same forms the order Cetiosauria, which he included under the sub- 
class Dinosauria: { ‘‘My fossil presents some remarkable differences 
from other figured Dinosaurian specimens, and I have thought it 
worthy of the attention of the Society, as indicating that distinct 
ordinal groups are probably confounded under the name Dinosauria. 
For if the skull be Dinosaurian which was figured by Mr. Hulke as 
probably that of /gwanodon (and of its Dinosaurian character I enter- 
tain no doubt), and the specimen now described be Dinosaurian, in the 
ordinary sense of the term, as I believe, then no one will doubt the 
propriety of placing the latter animal, with its indisputable lacertian 
characteristics, in a distinct ordinal group from the Wealden animal, 
which has the skull closed anteriorly in a way to which no Lacertilian 
makes an approximation. 
‘This difference is, indeed, in harmony with lacertian differences 
in portions of the skull in Cef#osaurus; so that had there been any 
*Inarecent publication by Lucy P. Bush Cardiodon is shown to have priority over Cetzosaurus. 
Am. Jour. Sc., Vol. xvi, p. 96. : 
+ Report British Association for the Advancement of Science, 1859, p. 164. 
Ty). <x..5, 0f London; Vol, (xxx, p.-690, 
