﻿444 
  H. 
  G. 
  SEELEY 
  OK 
  SOME 
  GENEBIC 
  MODIFICATIONS 
  

  

  sostinus, 
  Hawkins, 
  though 
  analogy 
  would 
  make 
  it 
  not 
  improbable 
  

   that 
  they 
  have 
  the 
  form 
  ascribed 
  to 
  them 
  by 
  Prof. 
  Owen. 
  This 
  

   doubt 
  existing, 
  the 
  type 
  of 
  the 
  pectoral 
  bones 
  of 
  the 
  genus 
  Plesio- 
  

   saurus 
  may 
  be 
  taken 
  from 
  the 
  fine 
  specimen 
  contained 
  in 
  Case 
  6 
  of 
  

   Eoom 
  III., 
  Forth 
  Gallery, 
  British 
  Museum, 
  at 
  present 
  named 
  PI. 
  

   Hawkinsii, 
  and 
  which 
  may 
  appropriately 
  be 
  left 
  so 
  named. 
  The 
  

   entire 
  animal 
  is 
  about 
  6 
  feet 
  6 
  inches 
  long, 
  and 
  has 
  the 
  arrange- 
  

   ment 
  of 
  pectoral 
  bones 
  which 
  I 
  here 
  figure 
  reduced 
  (fig. 
  8). 
  

  

  Fig. 
  8. 
  — 
  Pectoral 
  Arch 
  of 
  Plesiosaurus, 
  restored 
  from 
  Specimen 
  in 
  

   the 
  British 
  Museum. 
  

  

  I. 
  Interclavicle. 
  cl. 
  Clavicle, 
  s. 
  Scapula, 
  c. 
  Coracoid. 
  g. 
  Glenoid 
  cavity. 
  

  

  The 
  interclavicle, 
  which 
  is 
  very 
  small 
  in 
  PI. 
  triatar 
  sostinus, 
  only 
  

   just 
  emerging 
  in 
  front 
  of 
  the 
  coracoids, 
  in 
  this 
  species 
  is 
  seen 
  to 
  be 
  

   of 
  large 
  size 
  and 
  unusual 
  antero-posterior 
  extent 
  (I). 
  This 
  large 
  bone 
  

   extends 
  behind 
  the 
  coracoids, 
  much 
  as 
  the 
  interclavicle 
  extends 
  

   behind 
  the 
  hyosternal 
  bones 
  of 
  Chelonians, 
  and 
  posteriorly 
  shows 
  

   indications 
  of 
  a 
  median 
  cleft. 
  A 
  groove, 
  or 
  perhaps 
  a 
  suture, 
  di- 
  

   verging, 
  extends 
  therefrom 
  forward 
  and 
  outward, 
  most 
  clearly 
  seen 
  

   on 
  the 
  left 
  side 
  of 
  the 
  animal. 
  If 
  this 
  mark 
  indicates 
  separate 
  ossi- 
  

   fications, 
  which 
  were 
  distinct 
  in 
  early 
  life 
  and 
  have 
  become 
  anchy- 
  

   losed 
  with 
  the 
  interclavicle 
  in 
  mature 
  growth, 
  those 
  ossifications 
  

   would 
  probably 
  represent 
  the 
  hitherto 
  missing 
  clavicular 
  bones. 
  

   Similar 
  elements, 
  not 
  well 
  defined, 
  appear 
  to 
  occupy 
  corresponding 
  

   positions 
  in 
  the 
  large 
  pectoral 
  arch 
  of 
  the 
  animal 
  in 
  the 
  British 
  

   Museum, 
  named 
  by 
  Prof. 
  Owen 
  PI. 
  laticeps, 
  MS. 
  If 
  these 
  marks 
  

   do 
  not 
  indicate 
  the 
  union 
  of 
  clavicle 
  and 
  interclavicle, 
  then, 
  in 
  

   Plesiosaurus, 
  clavicles 
  have 
  no 
  existence. 
  

  

  I 
  proceed 
  now 
  to 
  describe 
  and 
  define 
  the 
  pectoral 
  characteristics 
  of 
  

   the 
  genus 
  Plesiosaurus. 
  

  

  Plesiosauktjs. 
  (Pig. 
  8.) 
  

  

  The 
  coracoid 
  bones 
  are 
  longer 
  than 
  broad, 
  chiefly 
  placed 
  behind 
  

   the 
  articulations 
  for 
  the 
  humeri, 
  but 
  also 
  extending 
  anterior 
  to 
  them, 
  

   contracting 
  in 
  breadth. 
  Part 
  of 
  the 
  curved 
  anterior 
  margin 
  contri- 
  

   butes, 
  with 
  the 
  interclavicle 
  and 
  a 
  scapula, 
  to 
  form 
  on 
  each 
  side 
  a 
  

   moderately 
  large 
  foramen. 
  The 
  coracoid 
  unites 
  with 
  the 
  scapula, 
  

   by 
  suture, 
  to 
  form 
  the 
  articulation 
  for 
  the 
  humerus. 
  

  

  The 
  scapulae 
  are 
  very 
  narrow, 
  concave 
  on 
  the 
  inner 
  border, 
  and 
  

  

  