[lambk] progress of VERTEBRATE PALAEONTOLOGY 23 



places the order Choristodera with equal rank to the Ehynchocephalia 

 in his subdivisions of the new siiperorder Diaptosauria, considering it 

 as a " sharply defined division of the Diaptosaiiria owing to its remark- 

 able parallelism with the Gavialoid Crocodilia," Champsosaurus and 

 Simœdosaums are the only known genera of the order, the former 

 ranging from the Belly Eiver series np to the Lower Eocene. 



Taking np the dinosaurs next in order, the forms from this horizon 

 fall into the two subordinal divisions of Theropoda and Orthopoda, 

 with few representatives of the first or carnivorous group, but with 

 many of the second, herbivorous dinosaurs, of the families of Stegosau- 

 ridœ, Ceratopsidœ and Trachodontidœ. The specialization noticeable 

 in both these suborders, leading to the total extinction of the entire 

 order at the close of the Cretaceous period is far advanced in the 

 Ornithomimidse and Ceratopsidse. The Stegosauridœ are already on 

 the wane, there being little evidence of their occurrence in rocks higher 

 than those of the Belly River series. 



Deinodon Iwrridus and Ornitliomimiis alius are carnivores, the 

 former classed with the Megalosauridœ, the latter with the family that 

 takes its name from the type genus and species, Ornithomimus velox, 

 from Colorado. Deinodon Iwrridus is closely allied to the Jurassic 

 Megalosaurus and also to its successor, Drijptosaurus, from the higher 

 Edmonton series. Known principally from teeth, additional material 

 and further study are necessary for a better understanding of its generic 

 relationships. Ornithomimus alius is a cursorial type with great grasp- 

 ing power in the manus, and is larger and shows greater specialization 

 than its supposed ancestor Ornitholestes Tiermanni, a lightly built 

 compsognathoid dinosaur recently described by Osborn from a nearly 

 perfect skeleton from the Como beds (Upper Jurassic) of Wyoming. 

 Among the characteristics of 0. alius may be mentioned the straightness 

 of the terminal phalanges of the pes, the great curvature and lateral 

 compression of those of the manus, the elongation and crowding to- 

 gether of the metatarsals and the remarkable development of the post- 

 zygapophyses of the caudal vertebrae, which have lost their neural spines. 



Palœoscincus asper and P. costatus, known from teeth, have been 

 doubtfully referred to the Stegosauria. Stereocephalus tutus is a very 

 heavily armoured Stegosaur of large size, with coossified plates protect- 

 ing the head, and transverse rows of postcranial keeled ossicles. On 

 this protective armour Stereocephalus no doubt relied in a great measure 

 for immunity from the attacks of its agile carnivorous contemporaries. 



The Ceratopsids Monoclonius belli, M. canadensis and M. dawsoni 

 are ancestral types of the much larger forms of Triceratops and Toro- 

 saurus from the Laramie. Siegoceras is a new type to which reference 



