﻿OF 
  THE 
  PLESIOSAURIAN 
  PECTORAL 
  ARCH. 
  445 
  

  

  straight 
  on 
  the 
  outer 
  border, 
  which 
  makes 
  a 
  sharp 
  angle 
  with 
  the 
  

   lateral 
  vertical 
  part 
  of 
  the 
  bone, 
  which, 
  arising 
  in 
  front, 
  widens 
  

   from 
  before 
  backward, 
  in 
  a 
  long 
  narrow 
  <j-shape, 
  to 
  the 
  articula- 
  

   tion, 
  where 
  it 
  is 
  often 
  prolonged 
  as 
  a 
  spur 
  over 
  and 
  above 
  the 
  proxi- 
  

   mal 
  end 
  of 
  the 
  humerus. 
  The 
  scapulas 
  converge 
  anteriorly, 
  but 
  are 
  

   divided 
  from 
  each 
  other 
  by 
  nearly 
  the 
  whole 
  width 
  of 
  the 
  inter- 
  

   clavicle, 
  on 
  the 
  extreme 
  lateral 
  wings 
  of 
  which 
  they 
  rest. 
  

  

  The 
  interclavicle 
  is 
  large, 
  often 
  as 
  long 
  as 
  broad, 
  and 
  apparently 
  

   may 
  include 
  in 
  its 
  posterior 
  part 
  a 
  pair 
  of 
  subordinate 
  ossifications. 
  

   It 
  is 
  of 
  modified 
  V-shape, 
  being 
  concave 
  in 
  front, 
  with 
  concave 
  sides, 
  

   which, 
  converging 
  posteriorly, 
  are 
  prolonged 
  behind 
  the 
  coracoids 
  

   in 
  a 
  sharp 
  point 
  ; 
  the 
  lateral 
  wings 
  are 
  much 
  expanded. 
  

  

  The 
  other 
  British 
  animals 
  usually 
  referred 
  to 
  the 
  genus 
  Plesio- 
  

   saurus, 
  which 
  do 
  not 
  conform 
  to 
  this 
  type, 
  are 
  shown, 
  by 
  their 
  pectoral 
  

   girdles, 
  to 
  belong 
  to 
  the 
  Elasmosauridae, 
  typified 
  by 
  Prof. 
  Cope's 
  genus 
  

   Masmosaurus, 
  in 
  which 
  the 
  interclavicular 
  bone 
  is 
  entirely 
  wanting. 
  

   At 
  present 
  I 
  am 
  able 
  to 
  define 
  three 
  new 
  English 
  genera 
  which 
  

   seem 
  to 
  agree 
  in 
  this 
  negative 
  character 
  of 
  wanting 
  an 
  interclavicle 
  ; 
  

   they 
  are 
  : 
  — 
  Eretmosaurus, 
  founded 
  on 
  the 
  Plesiosaurus 
  rugosus, 
  of 
  

   Owen, 
  from 
  the 
  Lias, 
  in 
  the 
  British 
  Museum 
  ; 
  Colymbosaurus, 
  to 
  be 
  

   indicated 
  by 
  Plesiosaurus 
  megadeirus, 
  of 
  the 
  Kimmeridge 
  Clay, 
  in 
  

   the 
  Woodwardian 
  Museum 
  and 
  in 
  that 
  belonging 
  to 
  Marshall 
  Fisher, 
  

   Esq., 
  of 
  Ely; 
  and 
  Muramoscmrus, 
  from 
  the 
  Oxford 
  Clay, 
  indicated 
  

   by 
  a 
  new 
  species 
  in 
  the 
  collection 
  of 
  C. 
  E. 
  Leeds, 
  Esq. 
  

  

  I 
  have 
  seen 
  indications 
  of 
  several 
  other 
  genera, 
  which 
  may 
  here- 
  

   after 
  be 
  defined 
  ; 
  and 
  probably, 
  when 
  other 
  parts 
  of 
  the 
  skeleton 
  are 
  

   critically 
  examined, 
  the 
  number 
  will 
  be 
  increased. 
  

  

  Eretmosaurt/s, 
  g. 
  n. 
  (Fig. 
  9.) 
  

  

  Prof. 
  Owen 
  has 
  had 
  drawn, 
  with 
  more 
  than 
  usual 
  clearness, 
  in 
  

   the 
  ' 
  Monograph 
  of 
  Lias 
  Plesiosaurs,' 
  the 
  chief 
  characters 
  of 
  PI. 
  ru- 
  

  

  Fig. 
  9. 
  —Pectoral 
  Arch 
  of 
  Eretmosaurus, 
  restored 
  from 
  Specimen 
  in 
  

   the 
  British 
  Museum. 
  

  

  s. 
  Scapula. 
  c. 
  Coracoid. 
  g. 
  Glenoid 
  cavity. 
  

  

  gosus 
  ; 
  but 
  as 
  the 
  pectoral 
  bones 
  are 
  badly 
  preserved 
  in 
  that 
  speci- 
  

   men 
  from 
  the 
  Lias 
  of 
  Leicestershire, 
  it 
  is 
  only 
  after 
  some 
  study 
  that 
  

   I 
  venture 
  to 
  express 
  ideas 
  of 
  their 
  forms 
  and 
  relations. 
  There 
  may 
  

   be 
  a 
  little 
  doubt 
  as 
  to 
  whether 
  a 
  distinct 
  interclavicular 
  ossification 
  

   ever 
  existed 
  ; 
  but 
  if 
  such 
  a 
  bone 
  were 
  present, 
  which 
  another 
  speci- 
  

   men 
  disinclines 
  me 
  to 
  believe, 
  then 
  the 
  bone 
  has 
  entirely 
  lost 
  its 
  

   individuality 
  in 
  the 
  mature 
  animal, 
  and 
  is 
  blended 
  with 
  the 
  scapiilse, 
  

   just 
  as 
  the 
  scapular 
  bones 
  in 
  the 
  region 
  between 
  the 
  small 
  precora- 
  

  

  