Tol.  49.] 
285 
A  XEW  CAUXITOEOrS  DIXOSATJIi. 
crown  was  laterally  compressed,  with  trenchant,  serrated  ‘  fore-and 
aft  ’  edges,  and  a  sharp  point.  The  whole  crown  is  somewhat  re¬ 
curved,  and  its  outer  surface  shows  a  prominent  vertical  ridge 
continuing  to  the  summit.  The  marginal  serrations  are  relatively 
large,  and  set  obliquely  to  the  long  axis  of  the  tooth.  Prom  the 
deflection  of  the  symphysial  region  it  may  he  inferred  that  the  pre¬ 
maxillary  portion  of  the  cranium  was  likewise  bent  downwards. 
The  total  number  of  teeth  was  probably  about  22. 
The  hinder  fragment  (  PI.  XI.  figs.  2,  2  a )  calls  for  only  brief  notice. 
It  is  of  the  usual  Crocodilian  and  Dinosaurian  type,  with  the  sur- 
angular  forming  only  the  outer  wall  of  the  upper  portion  ;  while  a 
short  distance  in  advance  of  the  line  of  fracture  there  was  doubtless 
a.  vacuity.  The  quadratic  cavity  is  narrower  than  in  existing 
Crocodiles,  while  the  production  of  the  articular  element  behind  that 
cavity  is  also  less  :  both  these  features  being  characteristic  of  the 
Theropodous  Dinosaurs.  Moreover,  the  upper  margin  of  the  sur- 
angular  rises  considerably  above  the  plane  of  the  quadratic  cavity, 
which  is  likewise  a  feature  distinguishing  the  jaws  of  the  latter 
group  from  those  of  Crocodiles.  The  outer  surface  of  the  angular 
and  surangular  elements  is  pitted  in  a  manner  somewhat  similar  to 
Crocodilian  jaws. 
That  the  specimen  is  Archosaurian  there  can  be  no  question ; 
while  the  features  just  indicated,  together  with  the  declination  of 
the  alveolar  margin,  and  the  form  of  the  teeth  and  their  mode  of 
succession,  serve  to  differentiate  it  from  the  Crocodilians.  The 
absence  of  a  nredentary  element,  together  with  the  form  of  the 
teeth,  distinguish  the  specimen  from  the  Ornithopodous  Dinosaurs  : 
while  the  teeth  alone  are  sufficient  to  distinguish  it  from  the 
Sauropodous  section  of  the  same  order.  TCe  have,  therefore,  only 
the  Theropodous  group  of  Dinosaurs  to  which  to  refer  the  specimen  : 
and  as  its  characters  are  essentially  those  of  that  group,  the 
jaw  may  be  regarded  as  having  pertained  to  an  Oxfordian  repre¬ 
sentative  of  those  reptiles. 
Prom  the  large  size  of  the  jaw  and  its  solid  structure,  we  may 
safely  put  on  one  side  Gcdurus ,  Calamosaums.  and  their  allies  :  and 
its  dimensions  alone  will  probably  also  serve  to  distinguish  the 
specimen  from  Com psognathus.  On  the  other  hand,  the  jaw  under 
consideration  differs  from  the  mandibles  of  Megalosaurus  and  its 
allies,  not  only  by  its  inferior  dimensions,  but  likewise  by  the 
greater  number  of  the  teeth, 1  as  also  by  the  serrations  on  the  latter 
being  set  obliquely,  instead  of  at  right  angles  to  the  long  axis  of  the 
crown.  The  latter  feature  will  also  serve  to  distinguish  the  speci¬ 
men  from  Zanclodon  ( PZciteosaurus )  of  the  Trias  and  Lias,  in  which 
most  of  the  species  are  also  of  considerably  larger  dimensions.  Com¬ 
pared,  however,  with  Theeodontosaurus,  a  much  closer  resemblance 
will  be  found  to  exist.  Thus  in  Hi.  antiquus  the  number  of  lower 
teeth  is  21 :  each  of  these  teeth  being  characterized  by  the  oblique 
serrations,  and  the  prominent,  vertical,  recurving  outer  ridge,  which 
1  Marsh  gives  15  lower  teeth  in  Ceratosaurus,  which  is  identified  by  Cope 
with  Megalosaurus. 
