﻿AND 
  AYES 
  OF 
  NORTH 
  AMERICA. 
  45 
  

  

  pressed, 
  the 
  centra 
  much 
  longer 
  than 
  deep, 
  and 
  deeper 
  than 
  wide, 
  and 
  with 
  smooth 
  con- 
  

   cave 
  sides. 
  

  

  The 
  ribs 
  of 
  the 
  anterior 
  cervico-dorsal 
  region 
  are 
  inserted 
  directly 
  in 
  the 
  vertically 
  

   oval 
  pits 
  of 
  the 
  centrum. 
  Immediately 
  at 
  the 
  point 
  where 
  these 
  cease, 
  thin 
  transverse 
  

   processes 
  appear 
  to 
  arise 
  from 
  the 
  lower 
  edges 
  of 
  the 
  rib 
  pits. 
  They 
  form 
  a 
  continuous 
  

   series 
  with 
  the 
  ribs, 
  and 
  soon 
  rise 
  from 
  the 
  plane 
  of 
  the 
  lower 
  face 
  of 
  the 
  centrum, 
  and 
  

   are 
  directed 
  obliquely 
  downwards. 
  At 
  the 
  end 
  of 
  the 
  cervical 
  series 
  they 
  are 
  directed 
  

   nearly 
  vertically 
  downwards. 
  The 
  number 
  of 
  these 
  vertebrse 
  is 
  very 
  great, 
  the 
  anterior 
  

   diminishing 
  to 
  a 
  very 
  small 
  size, 
  the 
  whole 
  measuring 
  a 
  little 
  more 
  than 
  half 
  the 
  total 
  

   length. 
  

  

  Most 
  of 
  the 
  cervicals 
  possess 
  two 
  venous 
  foramina 
  below 
  ; 
  the 
  dorsals 
  two, 
  and 
  most 
  

   of 
  the 
  caudals 
  one. 
  

  

  The 
  resemblance 
  of 
  the 
  caudals 
  to 
  the 
  usual 
  type 
  of 
  Plesiosaurus, 
  is 
  seen 
  in 
  the 
  fact 
  

   that 
  each 
  bears 
  near 
  its 
  posterior 
  articular 
  aspect, 
  on 
  the 
  inferior 
  face, 
  a 
  pair 
  of 
  articular 
  

   surfaces, 
  for 
  chevron 
  bones. 
  Similar 
  vertebrse 
  had 
  been 
  described 
  by 
  Leidy 
  as 
  the 
  caudals 
  

   of 
  a 
  genus 
  he 
  called 
  Discosaurus; 
  the 
  study 
  of 
  the 
  present 
  genus 
  shows 
  that 
  they 
  are 
  

   really 
  of 
  the 
  caudals 
  of 
  the 
  allied 
  genus 
  Cimoliasaurus. 
  

  

  The 
  ribs 
  are 
  simple 
  headed 
  ; 
  the 
  abdominal 
  ribs 
  seen 
  in 
  Plesiosaurus 
  are 
  possibly 
  

   wanting, 
  as 
  none 
  were 
  found 
  by 
  the 
  discoverer 
  of 
  the 
  fossil, 
  after 
  a 
  careful 
  search. 
  

  

  The 
  end 
  of 
  the 
  muzzle, 
  with 
  symphysis 
  mandibuli, 
  was 
  preserved. 
  This 
  is 
  flat, 
  the 
  

   symphysis 
  rather 
  short, 
  the 
  premaxillary 
  grooved 
  at 
  the 
  intervals 
  between 
  the 
  dental 
  alve- 
  

   oli. 
  The 
  teeth 
  are 
  deeply 
  implanted, 
  with 
  small 
  pulp 
  cavity, 
  are 
  cylindric 
  and 
  furnished 
  

   with 
  nearly 
  straight 
  elongate 
  conic 
  crowns, 
  which 
  are 
  minutely 
  but 
  sharply 
  striate 
  to 
  the 
  

   tip 
  ; 
  the 
  ridges, 
  straight, 
  continuous. 
  There 
  are 
  no 
  indications 
  of 
  nostrils, 
  so 
  that 
  these 
  

   were 
  probably 
  posterior 
  and 
  near 
  the 
  orbits, 
  as 
  in 
  Plesiosaurus. 
  

  

  The 
  pelvic 
  arch 
  is 
  more 
  extended 
  than 
  the 
  scapular, 
  and 
  strongly 
  resembles 
  the 
  pelvic 
  

   arch 
  of 
  other 
  Plesiosauridse. 
  The 
  scapular 
  arch 
  is 
  peculiar; 
  the 
  claviculi 
  are 
  broad 
  flat 
  

   bones 
  resembling 
  the 
  pubes 
  of 
  certain 
  tortoises, 
  while 
  the 
  coracoicls 
  are 
  much 
  like 
  the 
  

   coracoids 
  of 
  Plesiosaurus. 
  

  

  The 
  scapular 
  arch 
  is 
  remarkable 
  for 
  the 
  resemblance 
  of 
  coracoids 
  to 
  those 
  of 
  Plesio- 
  

   saurus. 
  The 
  clavicles 
  have 
  a 
  greater 
  transverse 
  extent 
  than 
  the 
  former, 
  and 
  have 
  a 
  very 
  

   extensive 
  line 
  of 
  union 
  medially, 
  and 
  a 
  narrow 
  posterior 
  prolongation 
  which 
  meets 
  a 
  simi- 
  

   lar 
  anterior 
  one 
  of 
  the 
  coracoids, 
  separating 
  the 
  intervening 
  foramina. 
  They 
  appear 
  to 
  

   form 
  about 
  one 
  third 
  of 
  the 
  walls 
  of 
  the 
  glenoid 
  cavity, 
  and 
  have 
  a 
  constricted 
  base 
  as 
  in 
  

   some 
  Plesiosauria, 
  applied 
  to 
  the 
  extremity 
  of 
  the 
  coracoid. 
  The 
  form 
  of 
  the 
  glenoid 
  

   cavity 
  cannot 
  be 
  readily 
  ascertained 
  from 
  the 
  absence 
  of 
  the 
  scapula. 
  What 
  we 
  have 
  of 
  

  

  AMERI. 
  PHILOSO. 
  SOC 
  VOL. 
  XIV. 
  12 
  

  

  