482 



Dr. Baron Francis JYopc-sa — Cratcrosaurus. 



Seeley considered to be the surface of attachment for the alisphenoid. 

 The fractured surface of the diapophysis (^d.) is situated above and 

 laterally of the parapophysis, where Seeley located the ex-occipital 

 and the periotic ; and the neural spine {71.) rose from the blunt, 

 compressed, and broken ridge, which is well shown in Fig. 2 of 

 Professor Seeley's drawings, though not specially mentioned. 



All the bone of the vertebra of Craterosauriis situated below the 

 zygapophyses corresponds to the column-shaped part of the Stegosaurian 

 dorsal vertebrae between these and the neural canal. The more 

 dense nature of the tissiie at the bottom of this column-like part that 

 was supposed by Seeley to indicate the vicinitj" of the pterygoid 

 suture of the basisphenoidal hypapophysis, indicates according to 

 our new interpretation the proximity of the neural canal, for in all 

 Dinosaurs the walls of this canal are characterized by dense bony 

 tissue. 



Fig. 1. Craterosaurus pottonensis, Seeley ; part of neural arch in right side- 

 view (A) and back view (B), one-half nat. size. Lower Greensand: Potton. 

 [Type-specimen in Sedgwick Museum, Cambridge.] For lettering see Fig. 2. 



A curious feature worthy of note is that in the middle of the 

 column-like part, where jnost Stegosaurians show spongy bony matter, 

 our fossil is perfectly hollow. Two irregular openings with fractured 

 margins, the uneven surface of the hollow itself, and the much worn 

 and rolled nature of the whole specimen suggest, however, that 

 a great part of this cavity, if not the whole of it, may be due to 

 post-mortem decomposition. In this case the influence of plant-roots, 

 grass, moss, and water penetrating into small natural cavities of bones 

 lying on the surface of the ground needs specially to be taken into 

 account. 



Having decided the anatomical character and general systematic 

 position of the type-specimen of Craterosaurus, its generic position 

 has to be considered. The unusually high position of the zyga- 

 pophyses from the neural canal at once separates our fossil from 



