\ ‘ : 
168 FIELD COLUMBIAN MUSEUM. ; 
reason for suspecting that the Potton fossil belonged to the Cetiosauria, 
I should have felt no difficulty in regarding it as the base of a Cetio- 
Saurian cranium. . . .. Onthe whole, I regard the bone as indicating 
that in at least one Order of the Sub-class Dinosauria the bones of the 
base of the cranium were Rhyncocephalian rather than Avian.’’ 
In 1878 Marsh proposed to raise his previously established group 
Atlantosauridz to the rank of suborder, and to include in it the genera 
Atlantosaurus, Apatosaurus, Morosaurus, and Diplodocus.* ‘The suborder 
was Clearly defined with regard to American groups, but the European 
forms and their previous classification were ignored, although a num- 
ber of them clearly fall within the same family groups. 
In this way these three synonymous terms have been adopted and 
used by various writers. ‘‘Opisthoceelia’’ has the undisputed claim 
| to priority. As applied, it included as its characteristic representative 
Cardiodon, the best known of the European forms. In its primary 
significance it is descriptive of all the well known forms, both Euro- 
pean and American, which have since been included in the group. It: 
was followed by Haeckel and in part by Cope and Baur. The one 
objection which has been urged against the term is, that it was pro- 
posed to be applied to a subdivision of the Crocodilia. This ob- 
jection is not valid, since there are no opisthoccelous crocodiles 
with which the group can be confused. The homogeneity of the 
group according to the first definition was recognized when it was 
bodily transferred by Seeley into the Dinosauria, when it was defined 
as Sauropoda by Marsh, and when it was made an independent order 
by Baur. Its inclusion under the Crocodilia was designated at the 
outset as artificial; its present inclusion under the Dinosauria was 
regarded by Baur as equally artificial. If this be true, the same objec- 
tion will hold against the terms later applied. 
The term ‘‘Cetiosauria’’ has gained favor owing chiefly to the fact 
_ that it was offered as a subdivision of the Dinosauria and hence has 
coincided ‘more nearly with later classification. It was based upon 
a distinction between the Cetiosaurian and Iguanodon skull, but that 
distinction had been taken for ‘granted by earlier writers, and was 
only made necessary by Huxley’s erroneous reference of Cardiodon to 
the Iguanodontide. 
As regards the term “*‘Sauropoda,’’ it must be recognized that it 
was based upon a much more complete knowledge of the group, and 
as a result was much more clearly defined. But if we were to demand 
complete knowledge of structure and affinities, in support of a group 
name, very few genera and families now accepted would stand. 
* Am, Jour. Sc., Vol. xvi, p. 412. 
