98 THE EXTINCT BATRACHIA, REPTILIA 



The figure 29 is the result of the preceding considerations, but it is not to be consid- 

 ered as completely demonstrated. They all go to show the narrow and prominent form 

 of the abdominal region, which was associated with its posterior position, and the great 

 lengths of the femora. Fig. a is a front view of the pubis ; b is an internal view of the 

 ischium of Clepsysaurus. 



Dentition. — The teeth of this genus are very much smaller in relation to the size of 

 the animal than in Iguanodon. They bear enamel on one surface only, the external for 

 the inferior series as Leidy points out. Thus but one edge of the worn crowns is enam- 

 elled, and acts functionally like that of the anterior faces of the incisors of Rodents.' They 

 produce shear-like edges, cutting the vegetable food by a horizontal transverse motion. 



HADROSAURUS MIRABILIS, Leidy. 



Proceed. A. N. Sci., Phil., 1868, 199. 



Trachodon mirabilis, Trans. Am. Phil. Soc, XI, 1860, 140. Tab. 



Upper Jurassic Bad Lands of Judith River, Nebraska. 



Known from teeth, and perhaps vertebrae and phalanges. 



HADROSAURUS FOULKII, Leidy. 



Proc. Acad. Nat. Sci., Phil., 1858, 218, Cret. Kept. IT. S. 76, Tab. XII to XVII. 

 Cretaceous green sand, New Jersey. 



There are eight localities in the green sand of Cretaceous age in New Jersey, from 

 which I have seen portions of this species. 



HADROSAURUS ?OCCIDENTALIS, Leidy. 



Thespesius oecidenialis. Trans. Amer. Philoso. Soc, XI., I860, 151, tab. 

 ? Cretaceous Beds of Nebraska, between Moreau and Grand Rivers. 



Of this supposed species, Leidy says, "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." In this he refers to Hadrosaurus mirabilis, which Hayden 

 discovered in the Jurassic of Judith River, while the types of Thespesius were found by the same geologist, in a bed 

 with other vertebrates, mostly reptiles, which he determined to be of Miocene age. 



Now, the extreme improbability of this type occurring in a Miocene bed will occur to many palaeontologists, as 

 has to me. With the view of determining this point if possible, I instituted an examination of the forms brought by 

 Dr. Hayden from this locality, and first of that most characteristic animal, the Ischyr other ium, of Leidy. This, as 

 has appeared in the preceding pages, I believe to be a reptile, allied to Plesiosaurus, a conclusion which at once estab- 

 lishes the Mesozic age of the bed. It coincides with the presence of Hadrosaurus, in indicating Cretaceous or upper 

 Jurassic age. 



