452 The American Naturalist. [May, 
rate directed backwards; mandible without predentary bone; 
dentary without coronoid process; sacral vertebræ with ribs 
intervertebral; and diapophyses without connections with ribs; 
pubes directed forwards, and strongly united at the ends. 
The Iguanodontia appear in the Lias with all characters 
(Scelidosaurus), and form an absolutely isolated group so far. 
The nearest relations seems to be with birds rather than with 
any other groups of the Monocondylia. Whether the peculiar 
condition of the premaxillaries and the relations of the jugal to 
the maxillary, which remind us of the arrangement in mammals 
and some Theromora, indicates affinity to the ancestral forms of 
these groups, I am unable to say; but the fact that in mammals 
the pubis is also turned back has to be noticed. 
The Iguanodontia reach to the Upper Cretaceous, and show in 
Agathaumas and Diclonius their highest specialization. 
The Cetiosauria are confined to the Jurassic, Wealden, and Cre- 
taceous (Cambridge Greensand).* They seem to have their 
nearest relatives in the Belodontidz. The Crocodilia, with their 
peculiar pelvic arch, seem to be also related to this group. 
he Megalosauria extend from the Triassic to the Cretaceous. 
_ The skull is of the pattern of Paleohatteria of the Proganosauria 
and the Rhynchocephalia, and it seems very probable to-day that 
the Megalosauria have developed from the Rhynchocephalia. 
Protorosaurus seems to be in this line. 
~ The earliest reptiles doubtless go back to the Carboniferous, 
from which formation we do not know a single reptile so far. 
This is made probable by the existence in the Permian and 
Lower Triassic of different groups of Reptilia. : 
likely that birds began to be branched off already in B 
Lower Triassic, probably from a group which gave also ong” 
to the Iguanodontia; but to decide this question is not pos- 
sible to-day. I still believe with Hitchcock that a great no 
of the tracks in the Connecticut Triassic sandstone afe H*® 
tracks of true birds, not of any of the Megalosauria ane : 
to-day. All Megalosauria known have a long tail, and we ONS” 
aah metatarsals figured by Seéley of a Dinosaur from the Cretaceous Greensand 
not be distinguished from those of Morosaurus. 
It is very - 
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