﻿2G 



FOSSIL REPTILIA OF THE 



the tail than in the neck. 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 haemapophyses 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 haemapophyses. 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 11 inches in length, 9 inches in breadth 

 across the mastoids, 1\ 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, which, 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 

 rostratus 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 fossae are oblong, contracting anteriorly, and are there outwardly 

 rounded off j in length 5 inches ; in breadth, posteriorly, 3 inches. The subcircular 

 orbits are 2 inches in diameter. The narrow elliptical nostrils are 1^- 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 



