Hatchkr: Genera and Species of Trach(^L)ONtid.k. 379 



referred thcni 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 struc- 

 ture of the tooth of Trachodon different from those of Hadrosaurus, 

 together with the convexo-concave anterior caudals and the plano-con- 

 cave posterior caudal of Thespesius, in comparison with the biconcave 

 caudals of Hadiosaitrus, will be sufficient to separate generically the 

 New Jersey Dinosaurian from that of the Upper Missouri." I have 

 already remarked that we are now quite certain that the types of Tra- 

 chodon and Thespesius came from essentially the same horizon, but in 

 regard to the relative horizons of the western and New Jersey beds we 

 cannot be so sure. It would seem however that the New Jersey 

 Dinosaur came from a somewhat lower horizon than did the others, 

 and this supposition in connection with the anatomical differences 

 pointed out by Leidy, together with their wide geographical distribu- 

 tion, might be taken to indicate that the remains of Hadrosaiiriis per- 

 tained to an animal generically distinct from Trachodon. This how- 

 ever can only be determined by a comparison of the remains of 

 Hadrosaurus with the more recently discovered skeletons of Tracho- 

 don which have since been found in the same deposits in the west as 

 were the type specimens, though unfortunately they have been referred 

 to various genera such as Gonodon, Diclonius, Claosaurus, etc. 



Three years after publishing his " Cretaceous Reptiles of the United 

 States" Dr. Leidy became fully convinced of the generic identity of 

 Trachodon and Hadrosaurus. In a communication to the Philadel- 

 phia Academy of Sciences in 1868," he says, " Hadrosaurus Foulkii, 

 the bulky vegetable feeder, and contemporary of the rapacious Lcelaps 

 aquilunguis, was at most probably only specifically distinct from Tracho- 

 don mirabi/is, the teeth of which were found in association with those of 

 Dinodon, so that, according to the laws of nomenclature, as Trachodon 

 has priority of name, I suppose the first mentioned animal must be called 

 Trachodon Foulkii, though the names of Hadrosaurus Foulkii and H. 

 mirabilis would appear more appropriate for these powerful dinosaurs. 



" The best preserved tooth of those originally referred to Trachodon, 

 represented in Figs. 1-6 of the plate above cited, is identical in form 

 with those referred to Hadrosaurus, and differs only in the absence of 

 the rugulations of the lateral borders of the crown, and in some less 

 important points. 



•See Proc. Phil. Acad. Sci., l868, p. I99. 



