26 
FOSSIL REPTILIA OF THE 
the tail than in the neek. The pleurapophyses continue to articulate in part with the 
neural arch to the tenth or twelfth caudal vertebra ; the pleurapophyses are straight, 
and have gradually diminished to a length of 1^ inch in the tenth caudal ; they are 
flattened, and slightly expand towards the fore extremity, which, in the one above 
cited, there measures 10 lines across ; the haemapophyses are distinctly shown, those 
of each pair being separate, beneath the centrums of the seventeenth, eighteenth, and 
nineteenth caudals, forming part of that series where the neural spines are turned to 
the left. The first of these hcemapophyses has a length of 1 inch 9 lines, and a fore- 
and-aft breadth of 6 lines at its compressed, dilated, free extremity. The articular 
surface of the centrum of the twentieth caudal vertebra is exposed ; it is gently 
concave, with a central depression, 1 inch 3 lines in vertical and nearly the same in 
transverse diameter, with an inferior border bevelled off at the fore part, for the 
articulation of the heemapophyses. The ten terminal caudals show the lateral com- 
pression and flattening, with suppression, first of the posterior then of the anterior 
zygapophyses ; next of the neural spine, and, in the last three or four, of the neural 
arch itself. Traces of haemapophyses may be distinguished as far as the twenty-ninth 
caudal. This compression of the centrums would indicate, by cetacean analogy, some 
development of the terminal dermal expanse, but in a vertical, not horizontal, direction. 
Reckoning the dorsal series of vertebrae as twenty-four in number, it constitutes 
rather more than one third of the whole extent of the spinal column ; the thirty-four 
caudal vertebrae, of smaller proportions, constitute another third ; the twenty-four 
cervicals are rather less than a third. The skull is equal in length to three fourths of 
the neck and to one sixth of the entire skeleton. The total length of the vertebral 
column is 9 feet 9 inches, the total length of the skeleton being 11 feet 8 inches. 
The skull (Tabs. IX and XIII) is 1 foot II inches in length, 9 inches in breadth 
across the mastoids, 7^ inches across the back of the orbits, but here it appears to have 
been somewhat flattened out by pressure. It is 5 inches 3 lines broad in front of the 
orbits, 2 inches across the narrowest part of the snout, vdiich, from the fore part of 
the orbit, is 11^ inches in length, and expands at its extremity to a breadth of 
2^ inches. This is the proportion of the snout, which gives the peculiar and 
distinctive character to the present species of Plesiosaurus, and which suggested 
rosfratus as the specific name ; in fact, the head, from the aspect exposed, resembles 
rather that of the Muschelkalk Pistosaurus than that of any of our heretofore known 
Liassic Plesiosauri. 
The temporal fossse are oblong, contracting anteriorly, and are there outwardly 
rounded off ; in length 5 inches ; in breadth, posteriorly, 3 inches. The subcircular 
orbits are 2 inches in diameter. The narrow elliptical nostrils are I^ inch in advance 
of the orbits. The upper and hinder boundary of the cranium, formed by the 
bifurcate parietal, and strong, overlapping mastoids, is convex superiorly, expanding 
as it proceeds outward. The middle part of the parietal rises into a sharp crest 
