﻿AND 
  AVES 
  OF 
  NORTH 
  AMERICA. 
  209 
  

  

  The 
  species 
  are 
  as 
  follows 
  : 
  

  

  « 
  Articular 
  extremities 
  of 
  dorsal 
  vertebrae 
  depressed. 
  

   Cervicals 
  much 
  depressed 
  and 
  with 
  smaller 
  articular 
  faces 
  than 
  dorsals 
  ; 
  inferior 
  

   aspect 
  of 
  cervical 
  centra 
  keeled 
  medially 
  and 
  laterally. 
  b. 
  platyspondylus. 
  

  

  Dorsals 
  with 
  transversely 
  oval 
  cups, 
  less 
  depressed 
  and 
  less 
  elongate. 
  

  

  B. 
  FRATERNUS. 
  

  

  BAPTOSAURTJS 
  PLATYSPONDYLUS, 
  Marsh. 
  

  

  Macrosaurus 
  platyspondylus, 
  Marsh. 
  Proceed. 
  Amer. 
  Assoc. 
  Adv. 
  Science 
  (Salem), 
  I860. 
  Halisaurus 
  platyspov- 
  

   dylus, 
  Marsh, 
  Silliman's 
  Journ. 
  Sci. 
  Arts, 
  1869, 
  p. 
  395. 
  

  

  This 
  most 
  distinct 
  species 
  was 
  established 
  on 
  a 
  median 
  cervical, 
  and 
  an 
  anterior 
  dorsal 
  vertebra; 
  the 
  right 
  splenial 
  

   bone 
  with 
  its 
  concave 
  articular 
  face, 
  and 
  a 
  small 
  portion 
  of 
  the 
  base 
  of 
  the 
  skull. 
  A 
  coracoid 
  found 
  near 
  these 
  speci- 
  

   mens 
  probably 
  belonged 
  to 
  the 
  same 
  animal, 
  although 
  it 
  is 
  smaller 
  than 
  the 
  other 
  parts 
  of 
  the 
  skeleton 
  would 
  appa- 
  

   rently 
  indicate, 
  and 
  differs 
  considerably 
  in 
  form 
  and 
  proportions 
  from 
  the 
  corresponding 
  bone 
  in 
  both 
  Liodon 
  

   and 
  Clidastes. 
  The 
  splenial 
  bone 
  differs 
  from 
  that 
  of 
  Mosasaurus 
  in 
  the 
  form 
  of 
  its 
  articular 
  face, 
  and 
  in 
  being 
  more 
  

   overlapped 
  in 
  front 
  of 
  the 
  joint 
  of 
  the 
  dentary. 
  

  

  Through 
  the 
  kindness 
  of 
  Prof. 
  Marsh, 
  I 
  have 
  had 
  the 
  opportunity 
  of 
  making 
  the 
  present 
  observations. 
  Other 
  

   parts 
  of 
  the 
  description 
  are 
  copied 
  from 
  his 
  description 
  quoted 
  above. 
  

  

  The 
  cervicals 
  present 
  smaller 
  cup 
  and 
  ball 
  in 
  proportion 
  to 
  those 
  of 
  the 
  lumbars, 
  than 
  is 
  seen 
  in 
  any 
  other 
  known 
  

   Mosasauroid; 
  they 
  are 
  so 
  depressed 
  as 
  to 
  be 
  nearly 
  twice 
  as 
  broad 
  as 
  deep. 
  The 
  inferior, 
  horizontal 
  limb 
  of 
  the 
  diapo- 
  

   physis 
  is 
  prominent 
  below, 
  leaving 
  on 
  each 
  side 
  of 
  an 
  obtuse 
  median 
  keel, 
  a 
  lateral 
  shallow 
  concavity. 
  The 
  median 
  

   keel 
  scarcely 
  projects 
  beyond 
  the 
  lateral. 
  The 
  neural 
  arch 
  is 
  slightly 
  more 
  contracted 
  above 
  antero-posteriorly, 
  than 
  

   in 
  any 
  other 
  species, 
  hence 
  the 
  zygapophyses 
  are 
  more 
  prominent. 
  The 
  neural 
  spine 
  is 
  contracted 
  antero-posteriorly 
  

   and 
  much 
  elevated. 
  The 
  hypapophysis 
  is 
  on 
  the 
  posterior 
  portion 
  of 
  the 
  inferior 
  surface, 
  and 
  is 
  quite 
  prominent, 
  but 
  

   shorter 
  than 
  the 
  centrum. 
  The 
  posterior 
  dorsals 
  resemble 
  only 
  those 
  of 
  Liodon 
  validus 
  out 
  of 
  the 
  genus; 
  they 
  are 
  

   considerably 
  more 
  slender, 
  and 
  without 
  the 
  obtusely 
  keeled 
  form 
  of 
  the 
  inferior 
  face, 
  characteristic 
  of 
  the 
  latter. 
  

   The 
  dimensions 
  of 
  the 
  posterior 
  cervical 
  vertebra 
  are 
  as 
  follows: 
  

  

  Inches. 
  Lines. 
  

  

  Length 
  of 
  centrum 
  below, 
  2 
  6 
  

  

  Transverse 
  diameter 
  of 
  articular 
  cup, 
  1 
  8. 
  5 
  

  

  Vertical 
  diameter 
  of 
  articular 
  cup, 
  11. 
  

  

  Distance 
  from 
  centre 
  of 
  cup 
  to 
  middle 
  of 
  lateral 
  edge, 
  11. 
  

  

  Length 
  of 
  diajjophyses 
  below 
  lower 
  margin 
  of 
  cup, 
  5.5 
  

  

  " 
  " 
  hypapophysis 
  below 
  lower 
  margin 
  of 
  ball, 
  8. 
  

  

  The 
  dorsal 
  vertebra 
  has 
  no 
  trace 
  of 
  hypapophysis, 
  and 
  the 
  lower 
  surface 
  of 
  the 
  centrum 
  is 
  remarkably 
  flat. 
  The 
  

   anterior 
  downward 
  prolongations 
  of 
  the 
  diapophyses 
  still 
  project 
  below 
  the 
  centrum, 
  but 
  they 
  have 
  become 
  obtuse 
  pro- 
  

   cesses, 
  partially 
  separated 
  from 
  the 
  more 
  vertical 
  portion 
  of 
  the 
  diapophyses 
  by 
  a 
  notch. 
  The 
  following 
  are 
  the 
  more 
  

   important 
  dimensions 
  of 
  this 
  vertebra: 
  

  

  Inches. 
  Lines. 
  

  

  Length 
  of 
  centrum 
  below, 
  2 
  6. 
  

  

  Transverse 
  diameter 
  of 
  cup, 
  1 
  9. 
  

  

  Vertical 
  " 
  " 
  1 
  

  

  Width 
  of 
  neural 
  canal 
  below, 
  <>■ 
  

  

  " 
  between 
  extremities 
  of 
  anterior 
  zygapophyses, 
  2 
  3. 
  

  

  Length 
  of 
  diapophyses 
  below 
  lower 
  surface 
  of 
  centrum, 
  2. 
  

  

  AME1U0A. 
  PHILO. 
  SOC. 
  — 
  VOL 
  XIV. 
  53 
  

  

  