84 HADROSAURUS. 
living Reptiles there are vegetable feeders, such as the Jyuana and Amblyrhynchus, 
yet the teeth of these with their trenchant jagged borders, are adapted to lacerating 
or sawing instead of masticating the food. 
Several of the teeth of Hadrosaurus are nearly identical in form and details of 
structure with the specimen of a tooth discovered a short time previously to the 
former, by Dr. F. V. Hayden, in the Bad Lands of the Judith River. The tooth 
just mentioned, together with several other much worn specimens, I referred to a 
distinct genus under the name of Zrachodon, but I shall not be surprised to learn 
that future discovery determined Hadrosaurus and Trachodon to be the same.* 
Of the nine specimens of teeth preserved among the collection of remains of 
Hadrosaurus, seven are alike in form, and are supposed to have belonged to the 
lower jaw; the other ‘two, different from the former, are supposed to have belonged 
to the upper jaw. 
The teeth of Hadrosaurus were probably inserted in the jaws in the same manner 
as Dr. Mantell supposed to be the case in the /yuanodon, that is to say, with the 
enamelled surfaces of the crowns of the upper teeth directed outward, and of the 
lower teeth inward; an arrangement, as remarked by Dr. Mantell, which finds an 
analogy in the reversed position of the molar teeth of ruminating animals. 
The shape and markings of the teeth of Hadvosaurus appear to indicate that they 
were placed in much closer apposition with one another and their successors than 
in Jguanodon ; the arrangement in the former being very remarkable. In Jguano- 
don the teeth occupying a position in the functional series were succeeded by others 
fish, or as mammalian teeth from a diluvial deposit, and Dr. Wollaston alone supported him in the 
opinion that he had discovered the teeth of an unknown herbivorous reptile.” Finally, he adds, “ it 
was not until I had collected a series of specimens, exhibiting teeth in various states of maturity and 
detrition, that the correctness of my opinion was admitted either as to the character of the dental 
organs or their geological position.” 
1 The teeth referred to Trachodon were discovered by Dr. Hayden, in an estuary, fresh water 
deposit, which he calls the Bad Lands of the Judith River, situated on the upper Missouri River, 
near its source. In regard to the age of the deposit, the testimony derived from the fossils is 
of a conflicting character, but according to Dr. Hayden, the facts warrant the opinion that if the 
deposit is not an American representative of the Wealden of Europe, it is at least in part as old as 
the Cretaceous. Proc. Acad. Nat. Sci., Phil., 1856, p. 72. Trans. Am. Phil. Soc., Phil., 1859, p. 123. 
Among the collection of fossils, brought by Dr. Hayden from Western America, were several ver- 
tebree and a phalanx, which I have referred to a Dinosaurian with the name of Thespesius. The 
specimens were obtained from the Great Lignite formation of Grand River, Nebraska, which Dr. 
Hayden considers to belong to the Miocene Tertiary period. The phalanx mentioned nearly cor- 
responds in form and size with the proximal phalanx of the hind foot of Hadrosaurus, described in 
the preceding pages. Of the vertebra, the two larger specimens are anterior caudals, and are con- 
vexo-concaye ; the small one, a posterior caudal, is plano-concave. Had the remains of Thespesius 
and Trachodon been found in a deposit of the same age, I should have unhesitatingly referred them 
to the same animal, and I cannot avoid the suspicion that future investigation may determine them 
to be the same. Should such a determination prove to be the case, the minor details of structure 
of the tooth of Trachodon different from those of Hadrosaurus, together with the convexo-concave 
anterior caudals and the plano-concave posterior caudal of Thespesius, in comparison with the 
biconcave caudals of Hadrosaurus, will be sufficient to separate generically the New Jersey Dino- 
saurian from that of the Upper Missouri. For an account of Thespesius see Proe. Acad. Nat. Sci., 
Phil., 1856, p. 311, and Trans. Am. Phil. Soe., 1859, p. 151. 
