238 ON THE FOSSIL ICHTHYOSAURUS. 



that Is supported by the want of the rounded knuckle in the hume- 

 rus or arm-bone to fill the deep socket in which it was lodged. 



The hind paddles are of the same shape, but are much smaller 

 than the fore, and their terminal bones are lost. Of the tail, there 

 are only a few joints remaining : but, judging from the increasing 

 size of the vertebrae from the head to the pelvis, and by comparison 

 with other specimens, we may conclude that the tail, when entire, 

 was nearly as long as the body and head together. Its transverse 

 processes are jointed to the spine, and the spinous processes are very 

 broad and strong, indicating great power in this organ, as is observ- 

 ed in the Crocodile, with considerable extent of lateral motion, as in 

 fishes. 



The specific characters of the present specimen do not corresj)ond 

 to those of any of the species hitherto described. In the paucity of 

 its paddle bones it resembles the Ichthyosaurus plaiyodoji of other 

 geologists, and to the /. chieroUgostonus of Hawkins; but it differs 

 from it in the pointed form of its teeth, and in the number of its 

 dorsal vertebrae, that amount to forty-eight or fifty, whereas the 

 vertebrae of the i. platyodon are only forty-four. It must, there- 

 fore, be considered as a new species ; and we would suggest the 

 name of /. macrorachis, as indicatin^^ its peculiar length of spine. 



Besides the loss of the tail, and of the extremity of the nose, 

 paddles, and of some of the ribs, the specimen presents the following 

 injuries : — the crown of the head is crushed flat, the bony plates of 

 the eyes are separated and dispersed, the jaws are pushed in contra- 

 ry directions, and one of the bones constituting the right side of the 

 lower jaw is broken. In the neck and back, the vertebrae are turn- 

 ed upon their axes, so that every rib is dislocated from its attach- 

 ment, the ribs of the left side of the neck being thrown in a bundle 

 forwards, while those of the body are very regularly disposed over 

 the spine, with their heads in contact with the spinous processes, 

 and their shafts lying diagonally across the right ribs that remain in 

 contact with, though disjointed from, the spinal column. Wherever 

 one bone has rested upon another, the superincumbent pressure has 

 been sufficient to crack and break the upper one at the point of con- 

 tact. This is the jase with most of the ribs of the left side, the 

 furcula, the coracoid processes, and the thigh bones 



The hollow cup-like interstices of such of the vertebr£e as still 

 remain in contact, are lined with dog-tooth crystals of carbonate of 

 lime ; but wherever they are at all displaced, the interval is filled 

 up by the surrounding substance, now converted into limestone ; 

 and this is the case even with the most minute cracks and fissures 



