1883.] NATURAL SCIENCES OF PHILADELPHIA. 103 



Lacertilia^and no perforations either external or internal, in agree- 

 ment with the same type. The coronoid process is very large and 

 elevated, and its base, which is crescentic in section, is embraced 

 by the surangular, and is reached posteriorly by the anterior pro- 

 longation of the articular. lis posterior face is concave, and its 

 apex is curved anteriorl}', reaching the superior edge of the jugal 

 bone at the inferior border of the orbit. The angular bone forms 

 the internal border of the dental fossa, and extends to the 

 posterior edge of the splenial above. Below, it sends a prolonga- 

 tion forwards. The greater part of the external and inferior faces 

 of the ramus are formed by the surangular bone, which has an 

 enormous extent, far exceeding in size that of any known reptile. 

 It extends posteriorly to below the quadrate cot3'lus. Anteriorly 

 it spreads laterally, and unites with its fellow of the opposite side, 

 forming a short symphysis, and simulating a dentary. At the 

 base of the internal side of the ramns, it is separated Irom the 

 anterior prolongation of the angular by an open Meckelian groove, 

 which shallows out near the middle of its length. In correspond- 

 ence with this extent of the surangular, the splenial is enormously 

 developed, and contains the great magazine of teeth which I have 

 described as characteristic of this type.^ Its internal wall is very 

 thin, and adheres closely to the faces of the teeth, in the fossil, in 

 its present condition. This development and dentition of the 

 splenial bone distinguishes the Hadrosatiridse widely from the 

 Iguanodontidae. The dentary bone is a flat semicircular plate 

 attached by suture to the extremities of the surangulars. There 

 is no trace of symphysial suture, and the posterior border sends a 

 median prolongation backwards, which is embraced b}' the suran- 

 gulars. The edge of the dentary is flat, thin, and edentulous, and 

 closes within the edge of the premaxillary. 



The dentition is remarkable for its complexity, and for the dif- 

 ference in character presented by the superior and inferior series. 

 Leidy pointed out the character of the latter^ in the Hadrosaurvs 

 foulkei, and I have described the character of the superior denti- 

 tion in the genera Cionodon^ and Dicloniiis.* The teeth of both 



1 Bulletin U. S. Geol. Survey Territories, F. V. Hayden ; ill, p, 594-7. 

 May, 1877. 



^ Cretaceous Reptiles North America, 1864, p. 83. 



^ Vertebrata of Cretaceous formations of the West, 1875, p. 59. 



* Proceedings Philadelphia Academy, 1876, p. 250. 



