84 HADROSAURUS. 



living Reptiles there arc vegetable feeders, such as the Iijuana and Amhlyrhyndms, 

 yet the teeth of these with their trenchant jagged borders, arc 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 Avith several other much worn specimens, I referred to a 

 distinct genus under the name of Trachodon, but I shall not be surprised to learn 

 that future discovery determined Hadrosaurus and Trachodou 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 Iguanodon, 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 Hadrosaurus appear to indicate that they 

 were placed in much closer apposition with one another and their successors than 

 in Iguanodon; the arrangement in the former being very remarkable. In Iguano- 

 don the teeth occupying a position in the functional series were succeeded by others 



lish, 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 specinions, exhibiting teeth iu 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." 



' The teeth referred to Trachodon were discovered by Dr. Haydeu, 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 Weaklen of Europe, it is at least in part as old as 

 the Cretaceous. Proc. Acad. Nat. Sci., Thil., 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- 

 tebras and a phalanx, which I have referred to a Diuosaurian with the name of Tliespesius. 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 phalan.x mentioned nearly cor- 

 responds in form and size with the pro.ximal phalanx of the hind foot of Had7-osaurus, described iu 

 the preceding pages. Of the vertebrae, the two larger specimens are anterior caudals, and are con- 

 ve.xo-concavo ; the small one, a posterior caudal, is plano-concave. Had the remains of Tliespesius 

 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 Tliespesius, in comparison with the 

 biconeavc caudals of ITadrosaurvs, will be sufficient to separate generically the New Jersey Dino- 

 : ;uiri:m from that of the Upper Missouri. For an account of Thespesitis see Proc. Acad. Nat. Sci , 

 J'hil,, 185(), p. 311, and Trans. Am. Phil. Soc, 1859, p. 151. 



