KIMMERIDGIAN DINOSAURS. 553 



centrum (ib., fig. 3) than in the anterior pair. The iij)per 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 Avhich such fossil shows to the Dinosaurian group. In the Crocodiiia 

 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.* 



In MegaJosaurus the lateral abutments for iliac attachments have diapophysial 

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

 cated in the sacral vertebrae of Iguanodon 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 PL 61, with figs. 3 and 4, ' Dinosauria,' PI. 12). In the sacral vertebra of 

 the Hglaosaurifs, above referred to, the duplex parapophyses have about the same develop- 

 ment as in BothriosponJglus. 



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

 cavities characteristic of the sacral vertebra; of the present genus ; whence I infer, from 

 the different relative expanse of the neural canal, as shown in the figures of the 

 vertebrae above compared, that the hind limbs were relatively less in Bothriospondglus 

 than in Iguanodon. They, probably, came nearer to Crocodilian proportions. 



A second more mutilated sacral centrum of Bothriosjjondglus (PI. 62, figs. 4, 5, 6) 

 shows the modification of that marked 4 in the sacrum of Hglaosaurus (' Dinosauria,' 

 PI. 38, figs. 1 and 2), in having the parapophysial expansion limited to one (?) on each side 

 of the centrum. In the present genus its base occupies the anterior half of the lateral 

 surface, instead of the smaller proportion shown in TlyJtsosaurus ; it is also more 

 depressed, and the entire centrum is flatter, though not in so great a degree as in the 

 subject of PI. 62 above described. Both ends of the present centrum are flat, and show a 

 greater proportion of the smooth unconfliient condition than in the subject of PI. 62, 

 fig. 3. The supporting parts of the neural arch forming the roofs of each lateral cavity 

 (PL 62,flgs. 4 and 5,/) are broken off together with the arch itself, and but a small part 

 of the neural surface (ib., flgs. 4 and 5, w) is preserved. 



This mutilation exposes the whole depth of the lateral excavations (ib., fig. 4,/,/) of 

 the centrum, undermining, as it were, the base of the neural arch ; and these show that 

 the breadth of the centrum beneath that arch is reduced, about midway between the two 

 ends, a and i, to half an inch, the breadth of the centrum at the fore end, a, being, when 



* See ' Crocodiiia, PI. Id, fig. (5, sacral vertebra of Crocodilus Haslingsice. 

 f See 'Dinosauria,' PI. 25. 



