174 CIMOLIOSAURUS RICHARDSONI. 



We can now sec the influence ocean-currents had, as they have 

 now, upon determining the temperature of the glol>e, and the con- 

 sequent disastrous effect upon cold-blooded reptiles when 

 suddenly lowered. We have not time to dwell further upon this 

 part of the subject, nor to show that Europe had not at the 

 commencement of the Tertiary age its present continental 

 character, but an insular one, giving free access to the polar 

 currents without the counteracting exchange of warm equatorial 

 currents. 



The nearly complete fossil before us belongs to that section of the 

 extinct reptilian class included in the Order Enaliasaurian or sea- 

 lizards, but subseqxiently divided by Sir Richard Owen, G.C.B., 

 F.R.S., into the Ichthynpteryyia and Sauropterygia ; the former 

 represented by the genera Baptanodon Optlialmosatmis anil 

 Ichthyosaurus, the latter by several genera. Until the year 

 1841 Plesiosaurus was the only representative of this order in 

 Great Britain. At that date Sir Richard Owen removed from it 

 two species, Plesiosaurus yrandis and Plesiosaurus trochanteinus, 

 under a new genus Pliosaurus. The fossils of this genus were 

 first founded upon two limbs, one of which is preserved in the 

 British Museum, the other in our County Museum. It had an 

 enormous head, supported by a short neck, in which it approached 

 the great freshwater Saurians of the present day, with charac- 

 teristic vertebrae, having a tubercular rising in the centre of the 

 centrum, and resembling Plesiosaurus in its fin-bones and elon- 

 gated phalanges. Their vertical range was restricted to the middle 

 and upper oolites, whereas Plesiosaurus extended from the Rh retic l)eds 

 right through to the chalk. Plesiosaurus is characterised by a very 

 long neck and a short tail. The vertebrae are deeper and more 

 solid than those of Ichthyosaurus ; the neural arches are anchylosed 

 with strong outstretched transverse blades to strengthen the spinal 

 column and to sustain the strain upon it in shallow water ; 

 coast-lines, estuaries, and rivers probably being the usual resorts 

 of these monsters. Their remains have been found in the 

 Wealden freshwater deposits. Ichthyosaurus, on the other hand, 



