1862.] 323 



transverse processes, as far as the fourth from the end. But the 

 antepenultimate had a long and slender transverse process on each 

 side ; the penultimate has an equally long but much stouter process, 

 while the last coccygeal vertebra has transverse processes of no less 

 length, and extremely stout. 



The expanded distal ends of these processes unite with one another, 

 and with the inner surfaces of the greatly expanded ischia. 



The ilia are immense quadrate bones, slightly concave anteriorly 

 and posteriorly, with their planes so directed as to form rather less 

 than a right angle forwards with the vertebral column. The crest 

 of each iliac bone is thick, expanded, and rugose, and so arched as 

 evidently to have afforded attachment and support to the carapace ; 

 which therefore rested directly, partly on the three transversely 

 disposed pillars afforded by the coccygeal vertebrae and the two 

 ischia, partly on the longitudinally arched crests of the sacrum and 

 of the thirteen dorsal or dorso-lumbar vertebrse, and partly on the 

 second great transverse support yielded by the arched crests of the 

 ilia. Apart from their anchylosis, the whole of the parts named 

 must have been practically fixtures in consequence of this arrange- 

 ment of the carapace ; and the only moveable parts of the vertebral 

 column must have been the tail (of which unfortunately no portion 

 has been found in the present specimen), posteriorly moveable on 

 the last coccygeal vertebra, the trivertebral bone with its two pair of 

 ribs, capable of an up-and-down motion on the foremost of the thir- 

 teen vertebrse, and then the cervicals, more or less moveable upon 

 the anterior part of the trivertebral bone and upon one another. 



I am not aware of the existence of any mammal in which the ver- 

 tebral column presents characters of a similar singularity. 



The mobility of the rib-bearing trivertebral bone, by a hinge-joint 

 upon the rest of the vertebral column, is peculiarly anomalous. How- 

 ever, if, as appears to have been the case, the heads of the ribs 

 attached to this bone were incapable of movement, and the first rib 

 was furthermore directly anchylosed with the sternum, respiration 

 must have been carried on entirely by the diaphragm, if the anterior 

 dorsal vertebrse had been immoveable on the posterior ones. The 

 hinge-like movement of the trivertebral bone, on the other hand, by 

 permitting the ribs and sternum to describe a longitudinal arc alter- 

 nately downwards and forwards, and upwards and backwards, would 



