THE 



GEOLOGICAL MAGAZINE 



NEW SERIES. DECADE V. VOL. IX. 



No. XL— NOVEMBER, 1912. 



I. — ISToTES ON British Dinosaurs.^ Part V : Craterosaurus 



(Seelet). 



By Dr. Bcaron FRANCIS NOPCSA. 

 f N the course of my researches among British Dinosaurs the kindness 

 1 of Dr. J. E. Marr and Professor T. McKenny Hughes has enabled 

 me to investigate closely tlie fragmentary bone which Professor Seeley 

 described in 1874 under the new generic name of Craterosaurus.- 

 Although the systematic position of the specimen had remained 

 problematical from the day of its discovery, nevertheless the hope was 

 entertained that in consequence of our present more ample knowledge 

 of Dinosaurs and fossil reptiles in general, it might now be possible 

 to determine the exact nature of tiiis appai'ently most interesting 

 fossil. The result was rather unexpected, for it became clear that 

 what Seeley supposed to be the base of a cranium was nothing else 

 than the neural arch of a dorsal vertebra showing the greatest 

 resemblance to the corresponding element in Stegosaurus. 



To prove the Stegosaurian affinities of Craterosaurus in a striking 

 and convincing manner, two drawings of the fossil are given side by 

 side in Fig. 1, together with corresponding figures of an American 

 -Stegosaurian vertebra in the British Museum (Natural History). As 

 shown by the figui'e (Fig. 2) of- the American Stegosaurus, Seeley's 

 supposed occipital condyle is a process formed by the two fused post- 

 zygapophyses (pt.z.), and the so-called base of the brain-cavity of 

 Craterosaurus corresponds exactly with the spoon-like projection that 

 is produced in Stegosaurs by the fusion of the two prse-zygapophyses. 



In consequence of the concrescence of the right and left anterior and 

 posterior zygapophyses, the cleft that is usually visible between the 

 zygapophyses of Reptilian vertebrae, but is already very much 

 oblitei'ated in Omosaurus Lennieri,^ is practically reduced to nothing 

 in Craterosaurus, so that a curious kind of zygosphenal articulation 

 is developed. 



Besides the, prae- and post-zj'gapophyses, one can also determine in 

 Craterosaurxis the position of the parapophysis, the diapophysis, apart 

 of the neurapophysis, and even the position of the neural canal. The 

 parapophysis [fa.^ is formed in Craterosaurus as in Stegosaurus by 

 a shallow well-marked depression, and represents the region which 



^ Part I, Hypsilophodon, Geol. Mag., 1905 ; Part II, Polacanthus, loc. cit. ; 

 Part in, Streptospmidylus, loc. cit. ; Part IV, Geol. Mag., 1911. 



" H. G. Seeley, " On a Lacertihan Cranium from the Potton Sands " : Quart. 

 Journ. Geol. Soc, vol. xl, pp. 690-2, 1874. 



^ Nopcsa, " Omosaurus Lennieri^' : Bull. Soc. Geol. Normandie, torn, xxx, 

 p. 11, anne 1910 (1911). 



decade v. — VOL. IX. — NO. XI. 31 



