﻿•54 
  1TR. 
  E. 
  LYDEKKER 
  ON 
  THE 
  REMAINS 
  AND 
  AEEINITIES 
  

  

  form, 
  it 
  remains 
  to 
  consider 
  its 
  generic 
  position. 
  At 
  the 
  time 
  

   when 
  I 
  first 
  brought 
  the 
  subject 
  of 
  this 
  part 
  of 
  my 
  paper 
  under 
  the 
  

   Society's 
  notice, 
  I 
  was 
  inclined 
  provisionally 
  to 
  employ 
  the 
  term 
  

   Plesiosaurus 
  in 
  the 
  wide 
  sense 
  in 
  which 
  it 
  has 
  been 
  used 
  by 
  Mr 
  

   Hulke. 
  Subsequent 
  experience 
  has, 
  however, 
  led 
  me 
  to 
  the 
  con- 
  

   clusion 
  that 
  it 
  is 
  advisable 
  to 
  separate 
  from 
  that 
  genus 
  not 
  only 
  those 
  

   Post-Liassic 
  forms 
  which 
  I 
  have 
  already 
  incidentally 
  mentioned 
  under 
  

   the 
  name 
  of 
  Cirnoliosaurus, 
  but 
  also 
  the 
  present 
  species 
  and 
  certain 
  

   kindred 
  forms. 
  I 
  shall 
  confine, 
  then, 
  the 
  name 
  Plesiosaurus 
  to 
  

   those 
  Sauropterygians 
  having 
  a 
  neck 
  of 
  considerable 
  length, 
  compa- 
  

   ratively 
  small 
  heads 
  and 
  teeth, 
  the 
  cervical 
  vertebras 
  more 
  or 
  less 
  

   elongated, 
  and 
  usually 
  with 
  double 
  costal 
  facets 
  and 
  firmly 
  anchylosed 
  

   arches, 
  and 
  the 
  pectoral 
  girdle 
  with 
  a 
  comparatively 
  large 
  omosternum, 
  

  

  Fig. 
  9. 
  

  

  Part 
  of 
  pectoral 
  limb 
  of 
  Peloneustes 
  philarchus. 
  (About 
  £.) 
  

   fe, 
  humerus 
  ; 
  t, 
  radius 
  ; 
  /, 
  ulna 
  ; 
  t\ 
  radiale 
  ; 
  i, 
  intermedium 
  ; 
  /', 
  ulna 
  e. 
  

  

  formed 
  of 
  two 
  elements 
  ; 
  the 
  scapulae 
  being 
  widely 
  separated 
  in 
  the 
  

   ventral 
  middle 
  line, 
  with 
  a 
  small 
  and 
  concave 
  ventral 
  surface, 
  and 
  a 
  

   very 
  large 
  dorsal 
  portion 
  extending 
  throughout 
  the 
  length 
  of 
  the 
  bone, 
  

   and 
  no 
  median 
  union 
  between 
  their 
  ventral 
  portion 
  and 
  the 
  coracoids. 
  

   In 
  those 
  forms 
  which 
  I 
  propose 
  to 
  include 
  in 
  Cimoliosaurus 
  the 
  

   neck 
  is 
  usually 
  greatly 
  elongated; 
  the 
  head 
  and 
  teeth 
  are 
  very 
  

   small 
  ; 
  the 
  cervical 
  vertebras 
  are 
  more 
  or 
  less 
  elongated, 
  with 
  single 
  

   costal 
  facets, 
  and 
  often 
  complete 
  anchylosis 
  of 
  the 
  arches 
  and 
  ribs 
  

   with 
  the 
  centra 
  ; 
  while 
  the 
  pectoral 
  girdle 
  is 
  devoid 
  of 
  an 
  omoster- 
  

   num, 
  and 
  has 
  the 
  ventral 
  part 
  of 
  the 
  scapulae 
  very 
  large 
  and 
  flat, 
  

   and 
  the 
  dorsal 
  part 
  greatly 
  reduced 
  in 
  size, 
  the 
  ventral 
  plates 
  

   meeting 
  in 
  the 
  median 
  line, 
  and 
  sending 
  down 
  a 
  median 
  bar 
  to 
  join 
  

   the 
  coracoids, 
  which 
  are 
  produced 
  in 
  the 
  middle 
  in 
  advance 
  of 
  the 
  

   glenoid 
  cavity. 
  This 
  genus 
  I 
  regard 
  as 
  a 
  branch 
  in 
  one 
  direction 
  

   from 
  Plesiosaurus, 
  while 
  another 
  branch 
  has 
  culminated 
  in 
  Plio- 
  

   saurus. 
  In 
  the 
  latter 
  branch 
  I 
  would 
  place 
  the 
  so-called 
  Plesio- 
  

  

  