SAUROPTERYGIA. 231 



but equally acute. In all the crown presents a body of hard 

 dentine, with a thin coat of enamel, as in the section above 

 the skull. There are no teeth on the extensive bony palate ; 

 and this shews no other apertures except the internal nostrils. 



The almost entire and undisturbed vertebral column, from 

 the muschelkalk of Bayreuth, figured by Yon Meyer in pi. 23 

 of his great work on muschelkalk Saurian s, and attributed 

 to Xothosaurus mirabilis, gives the earliest indication of that 

 modification of the trunk-bones which reaches its maximum 

 in the Plesiosaurus (fig. 93), in which it was first detected by 

 the sagacity of Conybeare* 



Twenty of the anterior vertebrae of this series, in Xotho- 

 saurus, which begins with the atlas, have the whole or part of 

 the rib-pit situated on the centrum as in the first vertebra in 

 fig. 90 ; the pit is wholly there on fourteen vertebrae ; it begins 

 to ascend upon the neural arch in the fifteenth, as in the second 

 vertebra, given in fig. 90, and is wholly placed there on the 

 twenty-first vertebra. 



• According, therefore, to the characters proposed f to dis- 

 tinguish the cervical from the dorsal vertebra, Xothosaurus 

 has twenty of the former. In the specimen referred to, 

 nineteen consecutive vertebrae shew the rib-pit supported 

 wholly on an outstanding diapophysis from the neural arch, 

 as in the third vertebrae in fig. 90 ; these are to be reckoned 

 therefore as dorsal vertebrae. In the cervical vertebrae the 

 rib-pit is large, vertically reniform, not divided by a groove ; 

 its circumference slightly projects in Xothosaurus. There is 

 no clear evidence of any of the cervical ribs being termi- 

 nally expanded and hatchet-shaped, as in Plesiosaurus ; those 

 of the back, £>l, are vertically longer than in Plesiosaurus, 

 and more convex. 



In the sacral vertebrae, fourth in fig. 90, the rib-pits again 



* Trans. Geol. Soc, vol. vi., 1822, and vol. i., 2d series, p. 381, 1824. 

 t Brit. Association, Report on British Fossil Reptiles, 1839. pp. 50, 58. 



