140 EXTINCT VERTEBRATA FROM THE JUDITH RIVER 
fact, that totally dissimilar animals have occupied different portions of the earth at the 
same period. The recent discovery of remains of the Hadrosaurus, another animal allied 
to the Jguanodon, in the Green Sand Formation of New Jersey, now inclines us to suspect 
that the Judith River Formation forms part of the great Cretaceous series of Nebraska, 
though we should not feel surprised if future explorations should determine it to be of 
Tertiary age. 
1. Ketinct Vertebrata from the Judith River Formation. 
SAURIA. 
TRACHODON MIRABILIS. 
With comparatively few exceptions, the living reptiles, whether turtle, saurian, serpent, 
or batrachian, are carnivorous in habit, and so far as we have been able to learn, such 
also appears generally to have been the case with the extinct forms of the same class, if 
we may judge from the anatomical structure of their remains. 
In all the living forms of reptile life, when they are in possession of teeth, these organs 
are observed to be constructed for the penetration and cutting of food, whatever the na- 
ture of the latter may be; and in no known instance are they adapted to the crushing or 
mastication of substances. Even in the family of Iguanians, in which we find genera, 
such as the Jgwana* of South America and the Amblyrhynchus of the Galapagos Islands, 
using exclusively vegetable food, the teeth with their trenchant, jagged crowns, together 
form an instrument adapted to cutting like a saw, rather than one intended to bruise sub- 
stances. | 
In the same category indicated in the preceding paragraph, it had been ascertained that 
all extinct reptiles belonged, until the discovery in the Wealden Deposit of England, by 
Dr. Mantell, of the great Jguanodon. It was therefore not at all surprising when the 
illustrious Cuvier first observed a tooth of the latter, that he pronounced it to be the in- 
cisor of a Lhinoceros, more especially as the specimen, which was in a much worn condi- 
tion, really bore a strong resemblance to the corresponding tooth it was supposed to be. 
Nor did the determination at the time excite any degree of wonder, though it was a matter 
of much surprise that remains of the Rhinoceros should have been found in a formation so 
ancient as the Wealden. 
Dr. Mantell afterwards, having sent a number of teeth of the Jguanodon for the ex- 
amination of Cuvier; the latter was led to remark,—“It is perhaps not impossible that 
they may belong to a saurian, but to one more extraordinary than any of which we pos- 
* In an Iguana tuberculata from St. Thomas, W.1., I found the stomach distended with vegetable matters 
alone, consisting of entire seeds, berries, fragments of soft stems, leaves and flowers. 
