﻿448 
  H. 
  G. 
  SEELEY 
  ON 
  SOME 
  GENERIC 
  MODIFICATIONS 
  

  

  riean 
  animal. 
  The 
  species 
  are 
  found 
  in 
  the 
  Oxford 
  Clay, 
  Ampthill 
  

   Clay, 
  and 
  Kimmeridge 
  Clay. 
  

  

  MuRJSNOSATTRTJS. 
  (Fig. 
  13.) 
  

  

  Both 
  pelvic 
  and 
  pectoral 
  arches 
  are 
  characterized 
  by 
  the 
  bones 
  

   having 
  no 
  median 
  antero-posterior 
  osseous 
  union. 
  Thus, 
  instead 
  of 
  

  

  Fig. 
  13. 
  — 
  Pectoral 
  Arch 
  of 
  Murasnosaurus. 
  

  

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

  

  two 
  obturator 
  foramina, 
  this 
  genus 
  has 
  but 
  one. 
  In 
  the 
  same 
  way 
  

   there 
  is 
  but 
  one 
  foramen 
  enclosed 
  between 
  the 
  scapulas 
  and 
  coracoids. 
  

   The 
  scapulas 
  converge 
  in 
  front 
  with 
  straight 
  anterior 
  margins, 
  which 
  

   make 
  a 
  right 
  angle 
  with 
  enormous 
  lateral 
  processes, 
  which 
  differ 
  

   from 
  those 
  of 
  all 
  other 
  Plesiosaurians 
  in 
  being 
  prolonged 
  forward. 
  

  

  With 
  these 
  characters 
  are 
  associated 
  a 
  union 
  of 
  the 
  neural 
  arches 
  

   of 
  vertebras, 
  only 
  comparable 
  to 
  that 
  seen 
  in 
  Serpents 
  and 
  Iguanoid 
  

   Lizards, 
  but 
  with 
  semicylindrical 
  zygapophysial 
  facets; 
  while 
  the 
  

   chevron 
  bones 
  join 
  tubercles 
  at 
  the 
  base 
  of 
  the 
  centrum 
  instead 
  of 
  

   articulating 
  between 
  two 
  centrums 
  ; 
  and 
  the 
  ulna 
  and 
  radius, 
  and 
  

   tibia 
  and 
  fibula, 
  are 
  distinct 
  in 
  form 
  from 
  those 
  of 
  other 
  genera. 
  

   The 
  type 
  of 
  the 
  genus 
  is 
  Murcenosaurus 
  Leedsii, 
  Seeley, 
  Q,. 
  J. 
  G. 
  S. 
  

   vol. 
  xxx. 
  p. 
  197. 
  I 
  should 
  place 
  the 
  Plesiosaurus 
  Oxoniensis 
  and 
  

   PI. 
  Manselli 
  in 
  a 
  subgenus 
  of 
  Murcenosaurus. 
  The 
  species 
  are 
  found 
  

   in 
  the 
  Oxford 
  Clay, 
  Ampthill 
  Clay, 
  and 
  Kimmeridge 
  Clay. 
  

  

  Rhomaleosaurtts, 
  g. 
  n. 
  

  

  One 
  genus, 
  found 
  in 
  the 
  Alum 
  shale 
  of 
  the 
  Upper 
  Lias 
  at 
  Whitby, 
  

   is 
  represented 
  by 
  the 
  fine 
  species 
  in 
  the 
  Museum 
  of 
  the 
  Royal 
  Dublin 
  

   Society, 
  which 
  has 
  been 
  named, 
  by 
  Mr. 
  Baily 
  and 
  Dr. 
  Carte, 
  Plesio- 
  

   saurus 
  Cramptoni. 
  This 
  type 
  has 
  given 
  no 
  evidence 
  of 
  its 
  sternal 
  

   bones; 
  but 
  its 
  other 
  characters 
  differ 
  so 
  far 
  from 
  those 
  usual 
  in 
  

   Plesiosaurus, 
  that 
  it 
  may 
  be 
  placed 
  in 
  a 
  genus 
  by 
  itself, 
  to 
  be 
  named 
  

   Rh 
  omaleosaurus. 
  

  

  The 
  cervical 
  vertebras 
  are 
  nearly 
  as 
  short, 
  from 
  back 
  to 
  front, 
  as 
  

   in 
  Pliosaurus 
  ; 
  and 
  the 
  cervical 
  rib 
  is 
  articulated 
  with 
  the 
  centrum 
  

   by 
  two 
  facets, 
  as 
  is 
  the 
  case 
  with 
  the 
  early 
  cervical 
  vertebras 
  of 
  

   Pliosaurus. 
  The 
  idna 
  and 
  fibula 
  have 
  not 
  the 
  usual 
  reniform 
  shape, 
  

   but 
  are 
  short 
  and 
  broad, 
  and 
  resemble 
  the 
  radius 
  and 
  tibia 
  in 
  being 
  

  

  