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MR.  R.  LYDEKKER  ON  THE  JAW  OF 
[Aug.  1893,- 
23.  On  the  Jaw  of  a  New  Carnivorous  Dinosaur  from  the  Oxford 
Clay  of  Peterborough.  By  R.  Lydekker,  Esq.,  BaA.,  F.G.S. 
(Read  March  22nd,  1893.) 
[Plate  XI.] 
I  am  indebted  to  my  friend  Mr.  A.  N.  Leeds,  of  Eyebury,  near 
Peterborough,  for  the  opportunity  of  bringing  under  the  notice  of 
the  Society  a  very  interesting,  although  unfortunately  imperfect, 
Dinosaurian  jaw,  recently  obtained  from  the  brick-pits  in  the  Oxford 
Clay  near  the  town  named. 
The  specimen  comprises  the  anterior  and  posterior  extremities  of 
the  left  ramus  of  the  mandible,  showing  the  alveoli  of  the  teeth  and 
the  cavity  for  the  articulation  of  the  quadrate.  The  fractured 
surfaces  are  fresh,  and  it  is  thus  evident  that  the  present  imperfect 
condition  of  the  specimen  is  due  to  a  blew  from  the  pick  of  the 
workman  by  whom  it  was  disinterred.  When  entire,  its  total  length 
was  probably  about  1  foot.  The  anterior  fragment  (PI.  XI.  figs.  1, 
1  ci)  comprises  the  greater  portion  of  the  dentary  bone,  with  the 
symphysis  entire ;  while  the  hinder  moiety  {ibicl.  figs.  2,  2  a) 
includes  the  articular,  and  portions  of  the  angular  and  surangular 
elements. 
The  dentary  bone  is  somewhat  roughened  and  pitted  on  its 
external  surface,  with  a  broad  symphysial  channel ;  while  the 
symphysis  itself  is  oblique,  and  in  life  was  evidently  united  by 
ligament.  Superiorly  the  outer  surface  is  concave  from  above 
downwards,  while  below  the  concavity  it  is  traversed  by  a  prominent 
longitudinal  ridge,  dividing  the  proper  lateral  from  the  inferior 
aspect.  The  alveolar  margin  is  characterized  by  its  abrupt  deflection 
near  the  middle  of  its  length :  the  deflected  portion  falling  away 
continuously  to  the  extremity  of  the  shallow  symphysis.  The  whole 
of  the  margin  in  question  is  penetrated  by  a  series  of  complete  dental 
alveoli,  which  extend  to  the  extremity  of  the  symphysis,  and  thus 
indicate  the  absence  of  any  predentary  element.  The  teeth  in  use 
at  the  time  of  the  death  of  the  animal  to  which  the  jaw  belonged 
have  entirely  disappeared  from  these  alveoli,  which  appear  to  be  19 
in  number.  Fortunately,  however,  a  replacing  tooth  is  apparent  in 
the  first  alveolus  ;  while  the  points  of  two  other  replacing  teeth  may 
be  observed  piercing  the  jaw  on  the  inner  side  of  the  alveolar 
margin  of  its  hinder  portion.  Indeed,  in  this  part  of  the  jaw  a 
row  of  small  cavities  running  parallel  to  the  main  line  of  alveoli 
indicates  the  presence  of  a  whole  series  of  these  replacing  teeth. 
This  mode  of  dental  succession — that  is  to  say,  the  new  teeth 
perforating  the  jaw  internally  to  those  they  are  to  replace,  and 
subsequently  breaking  into  the  main  alveoli — serves  at  once  to 
distinguish  the  specimen  from  the  jaw  of  a  Crocodile,  where  the 
replacing  teeth  come  up  immediately  beneath  those  in  use.  The 
tooth-germ  in  the  first  alveolus  (PI.  XI.  fig.  1  b)  shows  that  the 
