9 FOSSIL REPTILIA OF THE 
centrum, slightly projecting beyond the surface, and divided by a deep linear fissure. I 
have rarely seen an instance in which the neurapophyses were anchylosed to the centrum, 
and never one with the pleurapophyses so attached. In a specimen of Pliosaurus from the 
Kimmeridge Clay of Market-Downham, in the collection of C. B. Rose, Esq., F.G.S. 
(at Yarmouth), there are twenty of these short cervical vertebree, at the trunk end of which 
series the costal processes begin to climb, as in Plestosaurus, wpon the neurapophysis,—the 
diapophysis growing at the expense of the parapophysis, until the rib becomes supported, 
in the dorsal region, upon a single strong and prominent process: this is subdepressed, 
with an oval transverse section, which is rather sharp at the anterior margin. The verte- 
bral centrums begin to gain in length as the costal processes rise in position, and those of 
the dorsal region have attained to quite plesiosaurian proportions. Throughout the rest 
of the column the vertebra closely repeat the plesiosaurian characters on a large scale. 
The sides, or non-articular surface of the centrum, are rugous near the articular ends, 
elsewhere smooth, and in the dorsal region longitudinally concave. In the caudal 
vertebrae the costal process is undivided, prominent, with a vertically elliptical section, 
continuous with the neurapophysial surface at the base of the tail: the lower surface of 
the centrum is square-shaped and nearly flat: its angles are marked by the hypapophysial 
surfaces, of which the anterior pair is usually the largest.. 
The generic character derived from the organs of locomotion is the apparent absence 
of the antibrachial and cnemial bones, which seem to be represented by a proximal row 
of three large “carpal” and “tarsal” ossicles. On the homology of these I shall offer 
remarks in the sequel. 
As to the history of the present genus, I may briefly state that in a ‘Report on 
British Fossil Reptiles,’ communicated to the Meeting of the British Association for the 
Advancement of Sciences, held in 1839, and printed in the volume of ‘ Reports ’ for that 
year,* I described certain fossils, from which were deduced the two species of Plesvosaurus, 
called “grandis,” p. 83, and “trochanterius,” p. 85. In my second Report on the same class 
of fossils communicated to the Association in 1841, I pointed out (p. 60) the characters by 
which those two species departed so far from the type-characters of Plesiosaurus as to 
merit being placed in a distinct genus or subgenus, for which I proposed the name of 
Pliosaurus; admitting at the same time in reference to the two species, that “ subsequent 
discoveries and observations were needed to supply distinct and recognisable characters 
for them ”—‘ the two forms of femora, on which they were founded, not having then 
been found so associated with vertebrae and other bones as to aid in their definition.”+ 
I propose in the present Monograph to describe and figure the specimens, among 
those that have subsequently come under my notice, which afford good grounds for the 
acceptance of the two species, and for the addition of a third to the genus Pliosaurus. 
It may seem strange that jaws which have lost all their teeth should yield new characters 
derivable from the number, proportions, and disposition of such organs; but herein a 
* «Report of Brit. Assoc.,’ 8vo, pp. 83, 86, 1839. + Ib. (Second Report), p. 54, 1841. 
