﻿KIMMERIDGE CLAY. 



17 



surface of seven to eight lines. The surface is rough and slightly concave j it may have 

 contributed less than one half of the vertical extent of the sacro-iliac joint at this part. 

 The fractured or roughened surface above this parapophysis indicates a corresponding 

 diapophysial production of the neural arch for extension of the joint. Longitudinally 

 the pre-parapophysial surface slightly inclines toward the front articular surface, a, of the 

 centrum. This surface is flat, very rough, and irregular, indicative of having been 

 broken away from a partial confluence with the opposed surface of a contiguous sacral 

 element ; the lower part showing here and there a smoothness as of the original free sur- 

 face of this end of the centrum. Above this surface large unossified vacuities are shown 

 in the cancellous texture of the bone. The vertical diameter of the articular end of the 

 centrum is one inch three lines ; the transverse diameter is three inches six lines. The 

 lower margin is not entire, but has been eroded or worn away for an equable extent of 

 about four lines ; along the transverse curve it has not been broken off that end of the 

 centrum. 



The post-parapophyses (p') are shorter antero-posteriorly, thicker vertically ; and the 

 articular surfaces of this pair converge at a greater angle to the posterior surface, b, of the 

 centrum (ib., fig. 3) than in the anterior pair. The upper rough or fractured surface (fig. 

 3, n , n) may have coalesced with the fore part of the neural arch of the succeeding sacral 

 vertebra, if such arch, as in other Dinosaurs, has crossed the interval between its own 

 centrum and that of the next sacral. A greater extent of the hinder surface of the present 

 centrum (fig. 3, c), at its lower half, shows freedom from anchylosis than on the fore 

 surface. 



The Reptile indicated by the portion of the vertebra above described is referable by 

 the characters which such fossil shows to the Dinosaurian group. In the Orocodilia 

 the confluent outstanding parts of centrum and neurapophyses, affording attachment to 

 the pelvic arch, are single on each side of the sacral vertebra, and the neural arch 

 retains its normal position in connection with its centrum. 1 



In Megalosaurus the lateral abutments for iliac attachments have diapophysial 

 bases, or spring exclusively from the neural arch. 2 Pre- and post-parapophyses are indi- 

 cated in the sacral vertebrae of Ignanodon by the slightly produced or outstanding parts 

 of the side of the centrum articulating with the two displaced neural arches (compare figs. 

 1 and 2 of PI. Ill, with figs. 3 and 4, Tab. VII). 3 In the sacral vertebra of the 

 Hyl&osaurus, above referred to, the duplex parapophyses have about the same develop- 

 ment as in Bothriospondyhs. 



Not any of these earlier described Dinosduria have the flattened form and lateral 



1 See Tab. IX, fig. 6, sacral vertebra of Crocodilus Hastingsice, ' Monograph on the Fossil Reptilia of 

 the London Clay, &c.,' Part II, Palseontographical Society's volume for 1849. 



2 See Tab. I, ' Monograph of the Fossil Reptilia of the Wealden and Purbeck Formations,' Part III, 

 Palseontographical Society's volume for 1855. 



8 Monogr. cit., Part II, Palseontographical Society's volume for 1854. 



