MONOGRAPH (No. ITD 
OF 
Pt OSS th REPLIES 
OF THE 
KIMMERIDGE CLAY. 
Orper—SAUROPTERYGIA, Owen. 
Genus—PLtiosaurus, Owen. 
Tue first* and second+ Monoerapus relating to the Reptilia of the Kimmeridge 
Clay were mainly expository of the dental characters of Pliosaurus, and indicative of 
the gigantic size attained by some individuals of the genus. In the present Monograph 
I propose to treat of this genus more at large, and submit the evidences that I have 
obtained of its specific modifications. 
The generic characters of the teeth, in regard to shape and structure, have been 
sufficiently exemplified in the first two Monographs: those of the skeleton are chiefly 
shown by vertebra from the region of the neck. These resemble, at first sight, the 
vertebrae of the genus Jchthyosaurus in their extreme shortness as compared with 
their breadth and depth. A cervical vertebra of a Pliosaurus, from the Kimmeridge 
Clay of Foxcombe Hill, near Oxford, measures, for example, in breadth, six inches ; 
in depth, or vertical diameter, five inches; while in length, or the diameter corre- 
sponding with the axis of the animal’s body, or of its vertebral column, it measures 
only an inch and a half. Nevertheless, with these ichthyosaurian proportions is asso- 
ciated an essentially plesiosaurian type of structure. The lower surface of the cervical 
centrums show the pair of vascular foramina ; the terminal articular surfaces are flat, not 
concave : the cervical rib was ligamentously tied, in some species, to two processes, the di- 
and par-apophyses,—occupying two thirds of the fore-and-aft extent of the side of the 
* Vol. of Pal. Soc. for the year 1859; Monogr. of the ‘Reptilia of the Kim. Clay,’ pp. 15, 16, 
Pl. VII, 1861. 
+ Vol. of Pal. Soc. for the year 1860; Monogr. of the ‘Reptilia of the Kim. Clay,’ pp. 27, 28, 
Pl. XII, 1863 (1862 on the cover). 
l 
