ON BRITISH FOSSIL REPTILES. 77 



The general anterior concavity for the reception of the occipital tubercle 

 is formed at its circumference by the centrum and neurapophyses of the 

 atlas, and at its middle by the anterior detached odontoid epiphysis of the 

 axis, which is here evidently the analogue of the so-called atlas in the Ich- 

 thyosaurus, the true body of the atlas in the Teleosaur representing the first 

 inverted wedge-shaped bone in the Ichthyosaur. The spine of the atlas is 

 a large strong oblong piece, articulated with the neurapophyses of the atlas, 

 and partly overlapping those of the axis. 



The cervical vertebrae have strong transverse processes developed one 

 from each side of the centrum, and one from the base of each neurapophysis. 

 The posterior articular processes look obliquely downwards and outwards, 

 the anterior ones obliquely upwards and inwards. The spinous process is 

 compressed, its base coequal with the whole antero-posterior extent of the 

 neurapophysis ; its height equal to the distance from its base to the upper 

 transverse process; it inclines slightly backwards, and is slightly rounded 

 off at the summit. The cervical rib is bifurcate at its vertebral end, the 

 tubercle being as long as the head and neck ; its distal end is expanded into 

 the hatchet shape, the posterior angle being most produced, and overlap- 

 ping the costal process of the next vertebra behind. The same mechanism 

 for fixing and strengthening the neck thus existed for the advantage of the 

 ancient marine Crocodiles, as we find in those of the existing epoch. 



In the dorsal region the ribs exchange the hatchet for the ordinary length- 

 ened form, and soon begin to lose the head and neck, as in existing Croco- 

 diles ; after the fifth they no longer articulate with the central element, but 

 only to the transverse process of the neurapophysis, which increases in antero- 

 posterior extent and thickness, and pi-esents an oblique notch at its anterior 

 angle, for the reception of the tubercle, now the only head of the rib. The 

 number of the dorsal ribs exceeds that of any existing Crocodilian, being, 

 as above indicated, 16 pairs. The spinous process is proportionally strong ; 

 in the Whitby specimen it measures in most of the dorsal vertebrae 2 inches 

 in antero-posterior extent, and seven lines in transverse diameter or thick- 

 ness : the height of these spines seems not to have much exceeded that of 

 the cervical spines, but they are more truncated at the summit. 



A posterior dorsal or lumbar vertebra of a Teleosaur from the Whitby lias, 

 in the collection of Mr. Ripley, corresponds with the vertebral characters of 

 Telcosaurus in the slight concavity and circular contour of the terminal arti- 

 cular surfaces of the body, and in the great antero-posterior extent of the 

 spinous processes ; but that of the transverse process does not exceed one- 

 half the length of the body of the vertebra, which is 2 inches 6 lines. The 

 transverse process is supported by two short obtuse slightly-developed ridges, 

 which rise from the upper part of the side of the body, as far apart as to 

 include one-third of the length of the body between them, and converge to 

 the under part of tlie transverse process ; a similar ridge extends from the 

 upper part of the posterior end of the transverse process obliquely backwards 

 to the base of the posterior articular process. The neural arch is anchylosed 

 to the centrum in this vertebra. The supporting buttresses of the transverse 

 processes are not described by Cuvier in the dorsal vertebra; of the Ca<?n 

 Teleosaur ; nor have I met with any dorsal or lumbar vertebras of the Whitby 

 species, except the present, that was sufficiently perfect to exhibit tiiis cha- 

 racter; it may, however, be constant and characteristic of the genus. It 

 faintly indicates one of the most striking characters of the vertebrje of the 

 Slreptospondylus. The anterior and posterior margins of the spinous pro- 

 cess are slightly excavated, and thus retain a character which is transitory in 

 the Crocodile, and peculiar to an early period of its existence. 



