152 BRITISH FOSSIL REPTILES. 



CHAPTER V. Oeder— SAUROPTERYGIA, Owen. 

 Genus — Pliosaueus, Owen. 



In the genus of Sauropterygia called Plesiosaurus (ante, p. 1) the cervical 

 vertebra exceed in number and the neck in length those of other Saurian genera, 

 and the skull, so supported, is small in proportion. But, among the species 

 defined and described in the present volume (pp. 1 — 34), a certain range of variety 

 is exemplified in these respects. In Plesiosaums Iwmalospondijlus, for example 

 (pp. 12 — 20, Tab. V), the cervical vertebrse are thirty-eight in number, and 

 together include seven lengths of the skull. In Plesiosaurus rostratus (pp. 20 — 33, 

 Tab. IX) the same vertebras are but twenty-four in numljer, and together equal 

 only one and a half the length of the skull they support. 



The direction of specific modification here indicated gave warning of the 

 secondary importance of the cervical character, and at the same time suggested a 

 possibility of a still larger head with concomitantly shorter neck having been 

 engrafted on an essentially sauropterygian type of structure.' 



The discovery of certain fossil teeth which combined sauropterygian characters 

 with modified shape, and a size much exceeding that of any of those in the then 

 known Plesiosauri, led me to make them known as indicative of a distinct genus 

 under the name Pliosaurus." 



These teeth {Saiiropterngia, PI, 33, vol. iv) have a crown thicker in proportion 

 to their length and three-sided in shape, showing a subtriedral transverse section, 

 with one side flattened (ib., fig. 3), and bounded by prominent ridges from the 

 more convex sides, which are rounded oflf into each other, and alone show the well- 

 defined longitudinal ridges of the enamel (ib., figs. 1 and 2). 



The cervical vertebra (Sauropterygia, PL 18) are so compressed from before 

 backward (fig. 1) as to approach the ichthyosaurian type (pp. 45, 85, Tab. xvii, 

 xxix), but the articular surfaces are almost flat, (fig. 2) ; and though I have found 

 as many as twelve in one individual, they are so compressed as to cause a very 

 short neck to intervene between a large head and a massive trunk, in which the 

 dorsaUvertebrge resume the ordinary plesiosaurian proportions. 



1 See " Eemarks on this subject," in connection with a proposed Order called Macrotraclielen, by 

 V. Meyer, in my ' Palaeontology,' 8vo, 1851, pp. 252, 253. 



- ' Report on British Fossil Eeptilia,' Part ii, 1S41, in " Eeports of the British Association for the 

 Advancement of Science " for that year. 



