1891.] Remarks on Reptiles Called Dinosauria. 447 
nasal openings from which the maxillaries are excluded,' and the 
peculiar maxillary with the free posterior dentary end. 
From the study of the skulls alone it is evident that Iguanodon 
has to be separated entirely from Diplodocus and Ceratosaurus ; 
that there is no affinity whatever among these animals, which could 
permit us to place them in a common group may it be called a 
subclass or an order of reptiles. è. 
But I have to say exactly the same in regard to Diplodocus 
and Ceratosaurus. Diplodocus is of a crocodilian pattern, show- 
ing a well-developed alisphenoid; Ceratosaurus, however, is 
typically Rhynchocephalian or Proganosaurian in nearlý every 
detail, and it is certainly very much more related to these groups 
than to any other group of the so-called Dinosauria. The study 
of the skull alone would be sufficient to show that the Dinosauria 
is an absolutely unnatural group without any right of existence; 
it shows that the three members, Iguanodon, Diplodocus, and 
Ceratosaurus belong to three distinct groups of Monocondylia, 
with very little relation to each other. 
II. THE VERTEBRÆ. 
The vertebræ are of the character of the Archosauria, the 
dorsals having well-developed transverse processes. As is well 
known from the study of the Testudinata and* Crocodilia, the 
character of the articular faces of the centra of the vertebrz is of 
very little value in tracing the phylogenetic relation of groups. 
_The sacrum, however, shows peculiarities. 
[guanodon—In Iguanodon the sacral ribs are placed more or | 
less between the centra of the sacral vertebra. They are united to 
distinct diapophyses of the neural arches and to the centrum; 
the diapophysis may extend in some forms (Agathaumas) as far 
as the end of the sacral rib, but it is never separated from it. In 
other words, in Iguanodon the ilium is separated by sacral ribs, 
‘which are placed between the centra and to which diapophyses of 
the neural arches are suturally united or coéssified. 
1 This condition resembles very much that seen in mammals, in which aparra 
a process of the premaxillary extending between nasal and maxillary. irds the 
rey is Area from api n vpe pa the descending branches a eaa nasal. 
