HATCHER: OSTEOLOGY OF HAPLOCANTHOSAURUS 47 
armored and with all the many and diverse anatomical characters shown in their 
osteology which might reasonably be expected from such diversity of habits, there 
would seem good reasons for considering the Dinosauria as deserving of the rank of 
a subclass of the Reptilia comparable for example with the Metatheria of the 
Mammalia and divisible into three orders for each of which several names have 
been proposed by various authors. Of all these, those proposed by Marsh appear to 
the present writer to be the most appropriate, these are : 
1. THe THeropopa ; Hmbracing all the carnivorous dinosarus. 
2. THE Sauropvopa ; Hmbracing all the herbivorous forms in which the predentary is 
wanting. 
3. THE Prepentata; Hmbracing all the herbivorous forms im which the predentary 
is present. 
In accepting the terms Theropoda and Sauwropoda rather than Megalosawria and 
Cetiosauria I do so out of regard for the more comprehensive nature of those terms 
as used by Marsh. The latter terms as used originally by Fitzinger (Megalosawri), 
1843, and Seeley, 1874, respectively, I consider of subordinal rank only. Predentata, 
Marsh, is preferable to Orthopoda, Cope, because it is in no sense coordinate with the 
latter but a much more comprehensive term. Cope’s Orthopoda and the Ornithopoda 
of Marsh (not Huxley) are more nearly synonymous. 
Some authorities have considered the Sawropoda of Marsh (1878) as a synonym 
of the Opisthocelia of Owen (1859). But this appears to me quite unwarranted. 
For the latter term, although haying priority, was never adequately defined by 
Owen. It was originally proposed as a suborder of the Crocodilia’ and was char- 
acterized as embracing members of that group with opisthoccelous dorsal and cervical 
vertebrae. Owens’ original definition of the Opisthocelia was as follows: ‘The small 
group of Crocidilia, so called, is an artificial one based upon more or less of the 
anterior trunk vertebrae being united by ball-and-socket joints, but having the ball 
in front, instead of, as in modern crocodiles, behind.” As is now well known, the 
above character in no way distinguishes these dinosaurs from members of either the 
Theropoda or Predentata, and on the same page, in defining the order Dinosauria, 
Owen describes the cervical vertebree as being opisthoccelous in some species. It is 
thus clear that Owen not only did not adequately define his proposed suborder 
Opisthocelia, but that he did not recognize its real relationships as being with the 
Dinosauria rather than the Crocodilia. The character given distinguishes it from 
the Procelia or true Crocodilia, but should be considered as uniting it with, rather 
than separating it from, the Theropod and Predentate dinosaurs, for as has already 
7See Report 29th meeting Brit. Assoc, Ady. Sci., 1859, pp. 164, 165. 
