﻿

  S. 
  G. 
  SEEEEY 
  ON 
  NETTSTICOSAUETJS 
  PUSILLTJS. 
  355 
  

  

  supposing 
  that 
  we 
  may 
  have 
  here 
  to 
  do 
  with 
  a 
  second 
  species, 
  a 
  

   suggestion 
  which 
  is 
  supported 
  by 
  some 
  characters 
  of 
  the 
  tail 
  and 
  the 
  

   smaller 
  bones 
  of 
  the 
  limbs. 
  If 
  distinct, 
  however, 
  the 
  specimens 
  are 
  

   so 
  closely 
  allied 
  that 
  I 
  feel 
  justified 
  in 
  quoting 
  the 
  characters 
  of 
  one 
  

   as 
  illustrative 
  of 
  the 
  other. 
  

  

  In 
  nearly 
  all 
  Plesiosaurs 
  the 
  dorsal 
  rib 
  is 
  supported 
  upon 
  a 
  more 
  

   or 
  less 
  developed 
  tubercle 
  or 
  transverse 
  process. 
  This 
  type, 
  however, 
  

   shows 
  no 
  trace 
  of 
  any 
  such 
  character. 
  Each 
  centrum 
  is 
  4 
  mm. 
  long 
  ; 
  

   the 
  body 
  of 
  the 
  centrum 
  is 
  rounded 
  ; 
  and 
  instead 
  of 
  there 
  being 
  a 
  

   constriction 
  between 
  the 
  two 
  articular 
  ends, 
  the 
  centrum 
  is 
  slightly 
  

   inflated 
  in 
  the 
  middle 
  so 
  as 
  to 
  approximate 
  to 
  a 
  barrel-like 
  form. 
  

   Above 
  the 
  centrum 
  is 
  the 
  neural 
  arch, 
  generally 
  to 
  be 
  recognized 
  

   by 
  its 
  suture 
  ; 
  and 
  at 
  the 
  base 
  of 
  the 
  neural 
  arch, 
  where 
  it 
  ex- 
  

   pands 
  a 
  little, 
  is 
  the 
  articulation 
  for 
  the 
  rib. 
  And 
  while 
  the 
  rib 
  is 
  

   single-headed 
  as 
  in 
  Plesiosaurus, 
  the 
  ribs 
  themselves 
  have 
  a 
  Croco- 
  

   dilian 
  aspect, 
  because, 
  articulating 
  at 
  the 
  base 
  of 
  the 
  neural 
  arch, 
  the 
  

   slight 
  transverse 
  tubercle 
  indents 
  or 
  notches 
  them 
  out 
  above. 
  The 
  

   neural 
  arch 
  is 
  less 
  high 
  than 
  the 
  centrum; 
  it 
  is 
  oblong, 
  and 
  

   nearly 
  as 
  long 
  as 
  the 
  centrum. 
  Where 
  there 
  is 
  a 
  slight 
  displace- 
  

   ment 
  in 
  the 
  series 
  the 
  articular 
  end 
  of 
  the 
  centrum 
  appears 
  to 
  be 
  flat. 
  

   In 
  the 
  region 
  of 
  the 
  shoulder-girdle 
  several 
  centrums 
  appear 
  united 
  

   together 
  (PL 
  XIII. 
  fig. 
  1). 
  The 
  second 
  and 
  smaller 
  animal 
  only 
  

   exhibits 
  the 
  neural 
  aspects 
  of 
  the 
  vertebrae 
  (PI. 
  XIII. 
  fig. 
  3). 
  The 
  

   sides 
  are 
  divided 
  by 
  the 
  median 
  longitudinal 
  ridge 
  indicative 
  of 
  the 
  

   neural 
  spine, 
  which 
  may 
  be 
  a 
  trifle 
  broader 
  than 
  in 
  the 
  neck. 
  The 
  

   lateral 
  parts 
  of 
  the 
  neural 
  arch 
  are 
  transversely 
  expanded 
  and 
  some- 
  

   what 
  rounded 
  ; 
  each 
  neural 
  surface 
  is 
  once 
  and 
  a 
  half 
  as 
  wide 
  as 
  long, 
  

   has 
  its 
  anterior 
  margin 
  slightly 
  convex, 
  its 
  posterior 
  margin 
  concave, 
  

   its 
  lateral 
  margins 
  straight. 
  The 
  ridge 
  of 
  the 
  neural 
  spine 
  appears 
  

   to 
  be 
  prolonged 
  between 
  the 
  zygapophyses, 
  though 
  to 
  a 
  less 
  extent 
  

   than 
  in 
  the 
  neck. 
  There 
  is 
  no 
  sacrum 
  formed 
  by 
  union 
  of 
  vertebrae, 
  

   and 
  no 
  vertebra 
  that 
  can 
  be 
  recognized 
  as 
  sacral 
  from 
  any 
  modifi- 
  

   cation 
  of 
  structure 
  that 
  it 
  presents. 
  The 
  vertebra, 
  however, 
  imme- 
  

   diately 
  behind 
  the 
  ischio-pubic 
  suture 
  should 
  be 
  counted 
  sacral 
  ; 
  and 
  

   then 
  in 
  the 
  larger 
  specimen 
  there 
  would 
  seem 
  to 
  be 
  15 
  caudal 
  

   vertebrae. 
  At 
  least 
  13 
  caudal 
  vertebras 
  are 
  preserved 
  in 
  the 
  smaller 
  

   specimen 
  ; 
  but 
  they 
  correspond 
  in 
  form 
  and 
  size 
  to 
  the 
  first 
  8 
  in 
  

   the 
  larger 
  specimen, 
  and 
  obviously 
  are 
  only 
  a 
  portion 
  of 
  the 
  tail. 
  

   This, 
  with 
  some 
  differences 
  in 
  the 
  length 
  of 
  the 
  vertebrae, 
  would 
  

   again 
  suggest 
  that 
  the 
  specimens 
  may 
  belong 
  to 
  two 
  species. 
  

  

  In 
  the 
  larger 
  individual 
  the 
  tail 
  is 
  only 
  presented 
  on 
  one 
  

   side, 
  and 
  it 
  has 
  been 
  developed 
  so 
  as 
  to 
  show 
  the 
  transverse 
  

   processes. 
  The 
  second 
  centrum 
  behind 
  the 
  ischiac 
  bones 
  is 
  7 
  mm. 
  

   long. 
  The 
  transverse 
  process 
  arises 
  from 
  the 
  front 
  part 
  of 
  the 
  

   centrum, 
  and 
  is 
  broad, 
  compressed, 
  and 
  strong 
  ; 
  but 
  these 
  processes 
  

   become 
  rapidly 
  smaller 
  and 
  soon 
  disappear. 
  

  

  The 
  length 
  of 
  the 
  tail, 
  as 
  preserved, 
  reckoning 
  to 
  the 
  back 
  of 
  the 
  

   sacral 
  vertebra, 
  is 
  only 
  45 
  mm. 
  ; 
  and 
  although 
  it 
  may 
  have 
  extended 
  

   further 
  there 
  is 
  no 
  proof 
  or, 
  indeed, 
  reason 
  to 
  suspect 
  that 
  the 
  

   length 
  would 
  have 
  exceeded 
  5 
  cm. 
  In 
  the 
  second 
  specimen 
  the 
  

  

  