Diameters occipital condyle 



Cope ] ^44 ^May 6, 



Measurements of Skull No. 2. 



MM. 



Length of supraoccipital on middle line , 170 



Length of supraoccipital including occipital condyle 230 



Widtli of basioccipital posteriorly 155 



Width of foramen magnum 35 



vertical 40 



transverse 70 



Width of distal end of quadrate 135 



Total length of mandibular ramus 950 



Length of dentary above 480 



Length of fourth tooth from alveolus 55 



Width of fourth tooth at alveolus 27 



History. — I described this gigantic reptile in the Proceedings of the 

 Philadelpliia Academy for October, 1876, from teeth derived from the 

 Laramie formation of Montana, and afterwards {I. c. December, 1876, 

 p. 340), I described it more fully from a nearly entire dentary bone with 

 teeth from the same region. This individual did not differ much in dimen- 

 sions from those now described. 



Our knowledge of the structure of the cranium of the carnivorous 

 Dinosauria has been very slowly acquired. Buckland and Mantell orig- 

 inally knew only the mandibular rami, but Phillips much later obtained 

 a maxillary bone. From these fragments he proposed a restoration on 

 the basis of the skull of the Lacertilia, with but a single postorbital 

 bar. In this kind of restoration Prof. Owen coincided on the occasion 

 of his description of another maxillary bone in the Quarterly Journal, 

 Geological Soc. of London, 1883, p. 331. In a figure of a restoration, 

 he adopted the Lacertilian model instead of the Crocodilian, and he 

 therefore inserted a triangular postorbital, and an elevated coronoid ele- 

 ment. He also omitted the preorbital foramen. Dr. J. W. Hulke, at 

 that time President of the Geological Society, expressed the opinion, on 

 hearing Prof. Owen's paper, that Megalosaurus has two postorbital bars, 

 an anticipation proven to be correct at a later date. In 1884, Prof. Marsh 

 published a paper whicli contains a description of the skull of a species 

 of carnivorous Dinosaur which he calls Ceratosaurus nasicornis. While 

 this animal is probably a species distinct from the Megalosaurus buck- 

 landii,* it has not yet been shown to belong to a different genus. In this 

 paper the presence of a zygomatic arch like that of the Crocodilia is 

 demonstrated for this sole order, and the preorbital foramen is also de- 

 scribed. The general and more obvious characters of the cranium are 

 given, but many of those which are necessary for an exact understanding 

 of the position of the genus are not given ; especially are the characters 



*Amer. Jour. Sci. Arts, 1884, p. 330. It has been shown that the character on which 

 Prof. Marsh relied to distinguish the genus Ceratosaurus, and the family Ceratosauridse, 

 viz., the confluent metapodials, is pathological. The keeled process on the nose is prob- 

 ably only a specific character. 



