184  PEOF.  OWEN  ON  THE  SKULL  AND  TEETH  OF  THE  PLACODUS  LATICEPS. 
PLATE  X. 
Fig.  1.  Under  view  of  the  skuU,  with  the  dentition,  of  Placodus  laticejis. 
Fig.  2.  Inner  view  of  a portion  of  the  upper  jaw,  with  three  marginal  teeth,  of  Placodus 
gigas,  Agassiz. 
Fig.  3.  Grinding  surface  of  the  same  teeth. 
Fig.  4.  Outer  view  of  the  same  portion  of  jaw  and  teeth. 
Fig.  5.  Section  of  a tooth  and  part  of  the  jaw  of  the  same  specimen,  exposing  a forma- 
tive cavity,/*,  with  a successional  tooth,  d. 
Fig.  6.  Portion  of  mandible,  with  teeth,  oi  Placodus  pachygnathus,  Owen. 
Fig.  7.  Upper  view  of  the  teeth  in  the  same  fossil. 
PLATE  XI. 
Fig.  1.  Outside  view  of  a part  of  the  mandible  and  teeth  of  Placodus  batkygnathus. 
Owen. 
Fig.  2.  Grinding  surface  of  last  and  penultimate  tooth  of  Placodus  batkygnathus. 
Fig.  3.  Inside  \iew  of  the  dentigerous  part  of  the  mandible  of  Placodus  bathygnathus, 
exposing  part  of  a formative  cavity  and  tooth-germ,  b'. 
Fig.  4.  Under  view  of  the  skull,  with  the  dentition,  of  Placodus  rostratus  (Munstek, 
‘ Petrifacten-kunde,’  taf.  15). 
All  the  figures  are  of  the  natural  size : they  were  not  reversed  in  the  drawing,  so  that 
the  ‘ right  ’ in  the  text  and  specimens  is  the  ‘ left  ’ in  the  plates. 
