46 MEMOIRS OF THE CARNEGIE MUSEUM 
strongly favoring the including of them all in a single group, the Dinosawria. If on 
the other hand they were found to show little in common or were even more widely 
separated than are the later forms from the Jurassic and Cretaceous then there 
could be no reasonable grounds for considering the Dinosauria as a natural group 
and it would become necessary to discard that term, at least in the sense in which 
it is at present used. 
Since however as has been shown in Haplocanthosawrus, the Sawropoda and Pre- 
dentata do possess certain important anatomical characters in common and since in 
this the most generalized genus of the group at present known the relationships 
between these two groups are more apparent than in the more specialized genera, 
Diplodocus, Brontosaurus, etc. It is reasonable to suppose that in the yet undis- 
covered but still more generalized forms greater similarity in structure will be found. 
Moreover from our present knowledge the relationships between the Sawropoda, Pre- 
dentata and Theropoda, as has already been pointed out by Marsh, is indicated by 
a number of important characters possessed in common such as: 
“1. Teeth with distinct roots either fixed im more or less distinct sockets or in longitudi- 
nal grooves, never ankylosed, no palatal teeth. 
“2. Skull with superior and inferior temporal arches. 
“3. Double-headed cervical and thoracic ribs. 
“4. Sacral vertebre codssified and more numerous than in other reptiles, seldom less 
than five. 
“5. Tliwm extended in front of acetabulum, in the construction of which latter the ilium, 
ischium and pubis take part. : 
“6. Fibula complete. 
“7. The reduction in the number of digits commences with the fifth.” 
The present author is, therefore, of the opinion that the Dinosauria should be 
regarded as a valid and distinct group for the exact definition and description of 
which we must await further discoveries as also for definite proof that the different 
groups now included in it are actually related. 
Admitting that the Dinosauria do constitute a natural group we have next to 
consider the rank that should be accorded to it in any general scheme looking to a 
classification of the Animal Kingdom as a whole. Here again we find there has 
been great diversity of opinion. Without reviewing the various opinions that have 
at various times been expressed upon this subject it would appear to the present 
author, that, in consideration of the diversity in form, structure and habit which are 
found withing this group where some members are carnivorous and others herbiv- 
orous, some quadrupedal and others bipedal, some heavily armored and others un- 
