278 
ME.  E.  1YDEKKEE  ON  A  D3NOSATJEIAN  YEETEBBA 
[May  1893, 
accordingly  affords  a  strong  presumption  that  all  the  three  sets 
belong  to  one  and  the  same  species,  which  is  conclusively  shown  by 
the  present  specimen  to  be  quite  different  from  Hoplosaurus  armatus. 
The  vertebra  in  question,  which  probably  belongs  to  the  middle 
portion  of  the  dorsal  series,  has  lost  the  anterior  ball  of  the  centrum, 
and  the  upper  part  of  the  neural  arch,  the  base  of  the  transverse 
process  being  absent.  It  is  figured  from  the  left  side  in  fig.  1  (p.  277), 
and  for  comparison  I  have  added  a  reversed  reproduction  of  a 
portion  of  Mr.  Hulke’s  figure  of  the  dorsal  vertebrae  of  Hoplosaurus 
armatus ,  from  pi.  iv.  vol.  xxxvi.  of  this  Journal.  So  far  as  I  can 
determine,  both  vertebrae  occupied  nearly  the  same  position  in  the 
series.  There  is  no  very  great  dissimilarity  in  the  two  specimens, 
but  the  present  vertebra  is,  on  the  whole,  smaller  and  apparently 
relatively  shorter  than  the  other,  with  a  stouter  centrum.  In  the 
piesent  specimen  the  width  of  the  hinder  face  of  the  centrum  is 
about  t  inches,  and  its  height  6  inches  ;  the  corresponding  dimen¬ 
sions  of  the  other  specimen  being  approximately  7  and  5|  inches. 
The  most  obvious  point  of  distinction  between  the  two  vertebrae 
is  to  be  found  in  the  form  and  position  of  the  lateral  cavity.  In  the 
vertebra  of  Hoplosaurus  this  cavity  is  of  a  very  elongated  egg-shape, 
tapering  to  a  point  posteriorly,  and  it  is  divided  into  two  moieties 
by  a  vertical  partition  placed  some  distance  below  the  general  level 
ot  the  centrum.  These  two  moieties  are  of  nearly  equal  length, 
and  the  hinder  opens  directly  outwards.  The  total  length  of  the 
cavity  is  5|,  and  its  height  2^  inches  ;  and  the  lower  border  of  the 
hinder  moiety  reaches  to  within  2  inches  of  the  nearest  part  of  the 
lower  border  of  the  centrum. 
On  the  other  hand,  in  Mr.  Rufford  s  specimen  the  lateral  cavity 
(of  which  the  innermost  recesses  are  choked  up  with  ironstone)  is 
more  ear-shaped,  being  much  shorter  and  higher  than  in  Hoplo¬ 
saurus.  Moreover,  the  septum  between  the  two  moieties  is  placed 
close  to  the  posterior  end,  and  is  very  deeply  sunk.  In  consequence 
of  this  the  posterior  compartment  has  scarcely  any  lateral  extent, 
and  its  aperture  looks  nearly  directly  forwards,  so  that  the  portion 
seen  from  the  outside  forms  a  vertical  ellipse.  Then,  again,  above 
the  deeper  portion  of  the  anterior  end  of  the  cavity,  there  is  a 
shallow  depressed  area  which  is  totally  wanting  in  the  other  verte¬ 
bra  ;  while  the  cavity  is  bounded  anteriorly  by  a  vertical  wall  of 
bone  which  does  not  exist  in  Hoplosaurus.  The  length  of  the 
lateral  cavity  is  4J,  and  its  height  about  3  inches  ;  while  its  lower 
border  does  not  come  within  3  inches  of  the  level  of  the  lower 
border  of  the  centrum. 
Above  the  lateral  cavity  is  a  large,  triangular,  flat  surface  bounded 
by  ridges,  which  is  directed  more  upward  and  less  forward  than 
in  Hoplosaurus.  Moreover,  the  V  bounding  the  first  triangular 
hollow  on  the  side  of  the  arch  is  placed  much  more  forward  than 
in  the  latter.  There  are  also  differences  in  the  form  of  the  4  fore- 
and-aft  surfaces  of  the  two  bones,  into  which  I  need  not  enter,  as 
the  imperfect  condition  of  the  present  specimen  renders  them  diffi¬ 
cult  to  describe  satisfactorily. 
