﻿OF 
  THE 
  PLESIOSAHRIAN 
  PECTORAL 
  ARCH. 
  443 
  

  

  cimen 
  appears 
  to 
  be 
  transversely 
  divided 
  ; 
  and 
  Conybeare 
  lettered 
  

   tbe 
  anterior 
  piece 
  (the 
  piece 
  which 
  meets 
  the 
  interelavicle) 
  as 
  the 
  

   lateral 
  clavicular 
  bone. 
  Conybeare's 
  figure 
  and 
  interpretation 
  were 
  

   both 
  adopted 
  by 
  Cuvier, 
  except 
  that 
  the 
  bone 
  named 
  clavicle 
  and 
  

   scapula 
  is 
  regarded 
  by 
  Cuvier 
  as 
  so 
  singularly 
  placed 
  that 
  its 
  homo- 
  

   logy 
  needed 
  investigation. 
  

  

  The 
  author 
  of 
  the 
  article 
  " 
  Plesiosaurus," 
  in 
  the 
  ' 
  Penny 
  Cyclo- 
  

   paedia,' 
  in 
  reproducing 
  Conybeare's 
  figure, 
  named 
  the 
  whole 
  bone 
  

   clavicle, 
  and 
  supposes 
  that 
  the 
  upward 
  and 
  backward 
  process 
  of 
  the 
  

   bone 
  (not 
  seen 
  in 
  the 
  figure) 
  is 
  alone 
  to 
  be 
  named 
  scapula. 
  

  

  In 
  1834 
  Mr. 
  Hawkins 
  printed 
  his 
  memoirs 
  of 
  Ichthyosauri 
  and 
  

   Plesiosauri, 
  and 
  gave 
  therein 
  a 
  restoration 
  or 
  diagram 
  of 
  the 
  pec- 
  

   toral 
  bones, 
  professing 
  to 
  be 
  chiefly 
  drawn 
  from 
  the 
  specimen 
  which 
  

   he 
  named 
  Plesiosaurus 
  triatarsostinus 
  (a 
  species 
  with 
  three 
  conspi- 
  

   cuously 
  large 
  bones 
  in 
  the 
  tarsus), 
  which 
  Prof. 
  Owen, 
  for 
  the 
  inade- 
  

   quate 
  reason 
  that 
  there 
  may 
  be 
  one 
  or 
  two 
  more 
  small 
  bones 
  in 
  the 
  

   tarsus, 
  proposed 
  to 
  change 
  to 
  PI. 
  Hawhinsii. 
  Mr. 
  Hawkins's 
  name 
  

   has 
  fair 
  claim 
  to 
  retain 
  its 
  place 
  ; 
  for 
  to 
  Mr. 
  Hawkins 
  belonged 
  the 
  

   merit 
  of 
  recoguizing 
  the 
  species, 
  which 
  Dr. 
  Buckland, 
  who 
  was 
  likely 
  

   to 
  have 
  been 
  well 
  advised, 
  in 
  1836 
  confounded 
  with 
  PI. 
  dolichodeirus 
  

   in 
  his 
  ' 
  Bridgwater 
  Treatise,' 
  a 
  name 
  which 
  it 
  still 
  retains 
  in 
  the 
  last 
  

   edition 
  of 
  that 
  work. 
  But 
  in 
  the 
  pectoral 
  restoration 
  (fig. 
  7) 
  Mr. 
  Haw- 
  

   Pig. 
  7. 
  — 
  Pectoral 
  Arch 
  of 
  Plesiosaurus, 
  as 
  restored 
  by 
  Hawkins. 
  

  

  st 
  

  

  st. 
  Sternum. 
  cl. 
  Clavicle. 
  s. 
  Scapula. 
  g. 
  Glenoid 
  cavity. 
  

  

  kins 
  was 
  less 
  happy 
  ; 
  for, 
  naming 
  the 
  interelavicle 
  sternum 
  as 
  others 
  

   had 
  done 
  (and 
  as 
  it 
  theoretically 
  might 
  be), 
  he 
  regarded 
  the 
  scapulae 
  

   as 
  clavicles, 
  as 
  Prof. 
  Owen 
  subsequently 
  did, 
  while 
  the 
  coracoids 
  are 
  

   named 
  scapulae. 
  I 
  am 
  not 
  sure 
  whether 
  Prof. 
  Owen's 
  description 
  

   of 
  the 
  scapula 
  in 
  this 
  species 
  is 
  supported 
  by 
  evidence 
  ; 
  for 
  the 
  

   second 
  specimen 
  in 
  the 
  British 
  Museum, 
  named 
  PI. 
  Hawhinsii, 
  in 
  

   which 
  an 
  approximation 
  to 
  such 
  a 
  structure 
  is 
  seen, 
  certainly 
  might 
  

   be 
  separated 
  as 
  another 
  species. 
  These 
  species 
  being 
  regarded 
  as 
  

   the 
  types 
  of 
  the 
  genus 
  Plesiosaurus, 
  the 
  definition 
  of 
  the 
  genus 
  de- 
  

   pends 
  upon 
  the 
  accuracy 
  of 
  these 
  osseous 
  determinations, 
  if 
  generic 
  

   characters 
  are 
  to 
  be 
  drawn 
  from 
  the 
  pectoral 
  arch 
  ; 
  but 
  the 
  girdle- 
  

   bones 
  are 
  obscure 
  in 
  PI. 
  dolichodeirus, 
  and 
  the 
  scapulae 
  are 
  not 
  suffi- 
  

   ciently 
  excavated 
  to 
  determine 
  the 
  forms 
  of 
  the 
  bones 
  in 
  PI. 
  triatar- 
  

  

  2i2 
  

  

  