﻿50 
  ME. 
  R. 
  LYDEKKER 
  ON 
  THE 
  REMAINS 
  AND 
  AFFINITIES 
  

  

  The 
  symphysis 
  and 
  portions 
  of 
  the 
  rami 
  of 
  the 
  mandible 
  are 
  shown 
  

   in 
  Plate 
  II. 
  fig. 
  1. 
  In 
  its 
  very 
  long 
  symphysis 
  this 
  mandible 
  

   differs 
  widely 
  from 
  that 
  of 
  the 
  typical 
  Liassic 
  Plesiosaurus 
  dolicho- 
  

   dirus, 
  in 
  which 
  there 
  are 
  only 
  three 
  or 
  four 
  teeth 
  in 
  the 
  symphysis. 
  

   In 
  some 
  species 
  of 
  Plesiosaurus 
  (using 
  this 
  term 
  in 
  its 
  restricted 
  

   sense) 
  the 
  symphysis 
  tends, 
  however, 
  to 
  become 
  longer, 
  as 
  is 
  shown 
  

   in 
  the 
  jaw 
  of 
  P. 
  rostratus 
  of 
  Owen, 
  where 
  there 
  appear 
  to 
  be 
  six 
  or 
  

   seven 
  of 
  these 
  teeth. 
  No 
  Plesiosaurus 
  has, 
  however, 
  a 
  symphysis 
  

   of 
  the 
  length 
  of 
  that 
  in 
  the 
  present 
  specimen, 
  or 
  such 
  a 
  large 
  

   total 
  number 
  of 
  teeth. 
  In 
  both 
  these 
  respects 
  the 
  form 
  under 
  con- 
  

   sideration 
  agrees 
  much 
  more 
  nearly 
  with 
  the 
  type 
  mandible 
  of 
  the 
  

   genus 
  Pliosaurus, 
  figured 
  on 
  page 
  343 
  of 
  Phillips's 
  ' 
  Geology 
  of 
  

   Oxford,' 
  in 
  which 
  there 
  are 
  at 
  least 
  35 
  teeth, 
  of 
  which 
  some 
  12 
  

   are 
  included 
  in 
  the 
  symphysis. 
  Further 
  indications 
  of 
  Pliosaurian 
  

   affinities 
  are, 
  moreover, 
  shown 
  by 
  the 
  teeth 
  themselves, 
  of 
  which 
  an 
  

   entire 
  specimen 
  from 
  the 
  anterior 
  part 
  of 
  the 
  upper 
  jaw 
  is 
  shown 
  in 
  

   the 
  accompanying 
  woodcut 
  (fig. 
  4). 
  The 
  crown 
  of 
  this 
  tooth, 
  in 
  place 
  

  

  Pig. 
  4. 
  

  

  Upper 
  tooth 
  of 
  Peloneustes 
  philarchas. 
  (Nat. 
  size.) 
  

  

  of 
  being 
  regularly 
  conical, 
  with 
  the 
  flutings 
  running 
  continuously 
  

   from 
  base 
  to 
  summit 
  on 
  all 
  sides, 
  has 
  two 
  distinct 
  carinas 
  marking 
  

   off 
  a 
  lateral 
  surface 
  which 
  is 
  less 
  convex 
  than 
  the 
  rest 
  of 
  the 
  crown, 
  

   and 
  has 
  but 
  very 
  few 
  flutings, 
  or 
  ridges, 
  which 
  are 
  confined 
  to 
  the 
  

   basal 
  half. 
  On 
  the 
  more 
  convex 
  portions 
  of 
  the 
  crown 
  the 
  flutings 
  

   also 
  stop 
  short 
  of 
  the 
  summit, 
  and 
  are 
  of 
  the 
  bold 
  type 
  and 
  irregular 
  

   length 
  characteristic 
  of 
  Pliosaurus. 
  Although 
  these 
  teeth 
  are 
  de- 
  

   cidedly 
  different 
  from 
  those 
  of 
  the 
  typical 
  form 
  found 
  in 
  Pliosaurus 
  

   brachydirus, 
  yet 
  they 
  closely 
  resemble 
  in 
  structure 
  other 
  Pliosaurian 
  

   teeth 
  of 
  larger 
  size 
  from 
  the 
  Oxford 
  and, 
  more 
  rarely, 
  the 
  Kimeridge 
  

   Clay. 
  

  

  Several 
  teeth 
  from 
  the 
  Great 
  Oolite 
  of 
  Caen, 
  in 
  Normandy, 
  pre- 
  

   served 
  in 
  the 
  British 
  Museum 
  (No. 
  32608), 
  agree 
  almost 
  precisely 
  

   in 
  structure 
  with 
  those 
  of 
  the 
  present 
  form, 
  although 
  they 
  are 
  of 
  

   larger 
  size. 
  Similar 
  teeth 
  from 
  the 
  same 
  deposits 
  were 
  described 
  

   by 
  Deslongchamps 
  under 
  the 
  name 
  of 
  Poikilopleuron 
  Bucklandi 
  ; 
  

   but 
  their 
  Sauropterygian 
  character 
  was 
  pointed 
  out 
  by 
  M. 
  Sauvage*, 
  

   who 
  referred 
  them 
  to 
  his 
  genus 
  Liopleurodon, 
  of 
  which 
  the 
  type 
  species 
  

   may 
  be 
  included 
  in 
  Pliosaurus. 
  I 
  have, 
  however, 
  no 
  doubt 
  that 
  these 
  

   teeth 
  are 
  really 
  referable 
  to 
  Thaumatosaurus 
  oolithicus, 
  a 
  Sauroptery- 
  

   gian 
  from 
  the 
  Lower 
  Jurassic 
  of 
  Wiirttemberg, 
  described 
  at 
  a 
  much 
  

   earlier 
  period 
  by 
  Meyer, 
  of 
  which 
  more 
  anon. 
  

  

  The 
  cervical 
  vertebras 
  being 
  absent 
  in 
  the 
  Bedford 
  specimen, 
  their 
  

   * 
  Bull. 
  Soc. 
  Geol. 
  France, 
  ser. 
  3, 
  vol. 
  i. 
  p. 
  378 
  (1873). 
  

  

  