1918] The Ottawa Naturalist. 135 



ON THE GENUS TRACHODON OF LEIDY 1 . 



By Lawrence M. Lambe, F.R.S.C. 



Vertebrate Palaeontologist, Geological Survey, Canada. 



The generic term Trachodon first appeared in pala?ontological 

 literature in 1856 2 when Dr. Joseph Leidy used it in describing 

 teeth and tooth-fragments of herbivorous dinosaurs under the name 

 T. mirabilis. These teeth were discovered by Dr. F. V. Hayden 

 in the "bad lands" of Judith river, Montana (then included in Ne- 

 braska), U.S.A., in deposits which are now generally regarded as 

 synchronous, or nearly so, with the Belly River formation of Alberta, 

 Canada. This was the first descriptive reference to remains of the 

 North American Cretaceous herbivorous dinosaurs which have since 

 been usually referred to as constituting the family Hadrosauridae 

 (Trachodontidae) related to the Iguanodontidae of Europe, the two 

 families being classed under the suborder Ornithopoda of the Pre- 

 dentata. 



The identification of this genus is rendered uncertain by the 

 paucity of material on which it was established. 



Following the description of Trachodon in 1856, Leidy in the 

 same year described two caudal vertebra^ and a phalanx of a dino- 

 saur from the "Lignite formation of Grand river, Nebraska," (Lance 

 formation) under the name Thcspesius occidentalis. 



This genus rests on as unsatisfactory a basis as Trachodon as 

 inferences drawn from the type material, which in this case as in 

 Trachodon must be considered inadequate, have too great an element 

 of conjecture. 



The third genus, and the first to be founded on fairly compre- 

 hensive material was Hadrosaurus, established by Leidy in 1858 

 on remains from the Cretaceous marls near Haddonfield, New Jer- 

 sey. That Hadrosaurus, of which many bones of the skeleton as 

 well as teeth from both jaws, presumably of one individual, are 

 known, is not generically the same as Trachodon is most probable 

 when we compare the teeth of the former having papillated margins 

 and a rounded apex, with the smooth margined, sharply pointed tooth 

 of the latter. 



In 1860 s Leidy described the Judith river teeth at greater length 

 with good illustrations. Of the six teeth figured, two are nearly 

 complete, the other four are fragmentary. The tooth first mentioned 

 in the description (figures 1 6) is that of a hadrosaur. The last 

 one (figures 18 20) belongs to a ceratopsian, and three of the four 

 fragmentary ones are probably assignable to the Hadrosauridae. 



The close affinity of Trachodon, as represented by the meagre 



'Communicated with the permission of the Deputy Minister of Mines. 



-Proc. Acad. Nat. Sei. Phila.. vol. VIII, p. 72. 



3 Trans. Am. Phil. Soc. vol. XI, pp. 140-143, pi. 9, figs. 1-20. 



