110 FOSSIL REPTILIA OF THE 



characterised by nearly flattened articular extremities ; but although the vertebrae are 

 very variable in their proportions as to length and breadth in the different species of 

 Plesiosaurus, I have hitherto found none that combine the same antero-posterior 

 diameter with the nearly flattened, inferiorly converging, sides of the dorsal centrum, 

 as in the Iguanodon. When, however, the entire vertebra can be compared, or the 

 chief characters of the neural arch of the Iguanodon, with the tallying parts in the 

 Plesiosaurus, important differences present themselves. In the cervical region of the 

 Plesiosaurus, the neural arch is comparatively low and simple, and sends off no other 

 processes save the zygapophyses and spine : in the dorsal region a diapophysis is 

 superadded ; but this alone offers an articular surface for the rib, and there is not 

 any rudiment of parapophysis or of a parapophysial articulation for the head of the 

 rib, such as is shown at p, T. XXXV. In the presence of this lower transverse process 

 with the surface for the head of the rib, in the Iguanodon, developed either from the 

 side of the centrum (as in the anterior dorsal vertebrae), or from the side of the neural 

 arch (as in the middle dorsal vertebrae), we have a character* distinguishing it from 

 OpMdia, Lacertilia, and Enaliosauria, whilst in the strong bony platform, in which the 

 summit of the neural arch expands, with its supporting buttresses, we have an 

 additional character distinguishing it from all known Crocodilia ; and indicative of a 

 distinct order of reptiles. 



The importance of the characters deducible from Mr. Bensted's invaluable dis- 

 covery, will be plainly manifested when the detached vertebrae and other fragmentary 

 remains of large Saurians come to be described in the ' Monograph on the Wealden 

 Reptiles,' and I proceed next to notice those of some caudal vertebrae which are well- 

 preserved in the Maidstone specimen ; they are marked ' c. vertebrae" 1 in T. XXXIV, and 

 one of the most perfect is figured of the natural size in T. XXXVII. The centrum is 

 more compressed than in the trunk, its articular ends are less expanded, but the 

 flattened character of the inferiorly converging sides of the centrum being retained, 

 this part presents in a more marked degree the wedge-shaped figure ; the converging 



* First made known in my 'Report on British Fossil Reptiles,' Trans. Brit. Association, 1841, 

 p. 127. "In the interspace of the two buttresses of the anterior dorsal vertebree there is a large oval 

 articular surface, convex at the anterior, and concave at the posterior part, which has afforded a lodgement 

 to the head of the rib." The nature of the part affording this surface is described in the next page as 

 " the transverse process " which " extends from the side of the neurapophysis." At the commencement of 

 my 'Report' I defined the "transverse processes" as being "of two kinds, superior and inferior," (p. 48,) 

 but I did not, in that 'Report,' specify them by the names " diapophysis " and "parapophysis:" the 

 process in question for the head of the rib is the "parapophysis." The author of the Appendix to 

 Dr. Mantell's Paper, in the 'Philosophical Transactions,' 1849, assuming the " upper transverse process" 

 to be the one indicated in my description of the fractured vertebra, No. 2160, imputes to me what he 

 conceives to be an error (p. 291) ; but the error lies in his assumption. It is one amongst many instances 

 of tbe necessity of abandoning the vague term ' transverse process,' and the advantage and propriety of the 

 definite names "diapophysis" and "parapophysis," which I have been in the habit of using since the 

 publication of my ' Report ' in 1 84 1 . 



