[ 169  ] 
IX.  I)escn])tion  of  the  Skull  and  Teeth  of  the  Placodus  laticeps,  Owen,  with,  indications 
of  other  new  Sjjecies  of  Placodus,  and  evidence  of  the  Saurian  Nature  of  that  Genus. 
Ty  Professor  Owen,  Superintendent  of  the  Natural  History  Departments 
in  the  British  Museum. 
Eeceiyed  Febraary  6, — Bead  March  11, 1858. 
Count  Munster,  in  the  year  1830,  obtained  two  specimens  of  portions  of  the  upper 
jaw  with  the  palate  and  teeth,  of  a vertebrate  fossil,  from  the  Muschelkalk  member  of 
the  Triassic  system  near  Bayreuth,  which  he  described  and  figured  in  a brochure, 
entitled  “ Fossile  Fischzahne  von  Bayreuth^,”  referring  the  specimens  to  the  class  of 
Fishes.  They  were  chiefly  remarkable  for  the  large  size,  and  especially  the  breadth  and 
shortness,  of  the  crowns  of  the  teeth. 
Professor  Agassiz,  in  the  ‘ Part  ’ of  his  great  work  on  Fossil  Fishesf,  which  appeared 
in  1833,  and  formed  the  commencement  of  the  second  volume,  accepted  Count  Mun- 
ster’s detennination  of  the  foregoing  fossils,  referred  them  to  the  Pycnodont  family  of 
the  Ganoid  order  of  his  System  of  Ichthyology,  and  founded  on  them  a genus  which  he 
called  Placodus,  a term  significant  of  the  broad  fiat  teeth  of  such  supposed  fishes.  The 
generic  character  given  by  Professor  Agassiz  is  as  follows : — “ Dents  polygenes,  a angles 
arrondis,  dont  la  surface  est  aplatee  et  entierement  lisse;”  and  he  adds,  “ Eange  par 
induction  dans  I’ordre  des  Ganoides ; car  je  n’ai  jamais  vu  les  ecailles  d’aucun  poisson  de 
ce  genre  I ” Of  this  genus  he  defines  two  species : — 
1.  Placodus  impressus,  Ag.  ; characterized  by  a depression  on  the  middle  of  the  crown 
of  the  tooth,  from  the  triassic  formation  called  ‘ gres  bigarre,’  at  Deux  Ponts. 
2.  Placodus  gigas,  Ag.  ; characterized  by  the  flat  crown  of  the  teeth : from  the 
Muschelkalk,  Bayreuth.  This  species  is  founded  on  the  specimens  originally  described 
by  Count  Munster. 
Professor  Bronn,  in  his  ‘ Lethsea  Geognostica,’  adopts  the  systematic  position  assigned 
by  Professor  Agassiz  to  the  genus  Placodus ; but  he  remarks  that  it  is  known  by  little 
more  than  the  teeth,  which  are  all  short  and  almost  flat,  from  four-  to  six-sided,  with  the 
angles  rounded  off;  and  he  states  that  the  vertebral  column  and  scales  are  unknown. 
Three  species  of  Placodus  are  admitted  in  this  work^J;, — Placodus  impressus,  Agassiz, 
from  the  Bunter-sandstein  of  Zweibriicke  (Deux  Ponts) ; Placodus  gigas,  Agassiz,  from 
the  Muschelkalk  of  Bamberg  and  Bayreuth ; and  a third  species,  afterwards  called  Pla- 
* Fossile  Fiscbzahne  von  Bayreuth,  4to.  1830. 
t Recherches  sur  les  Poissons  Fossiles,  tome  ii.  1833-43. 
+ Band  i.  8vo,  1837,  p.  186.  tab.  13.  fig.  13. 
2 A 
MDCCCLVIII. 
