170 
PROrESSOE  OWEX  OX  THE  SKULL  AXD 
codus  Andriani  by  Agassiz,  from  the  Muschelkalk  of  Laineck,  near  Bamberg.  In 
another  part  of  the  first  volume  of  the  ‘ Lethaea  Geognostica  teeth  of  Placodiis  are  cited 
with  those  of  other  Ganoid  fishes,  in  an  enumeration  of  the  fossils  of  the  ‘ Salz-gebu'ge  ’ 
(Muschelkalk  and  Keuper  divisions  of  the  Trias). 
In  1841  I gave  a brief  summary,  in  the  section  of  my  ‘ Odontography  ’ on  the  teeth 
of  Pycnodonts,  of  the  descriptions  of  the  dentition  of  Placodus  from  the  wTitings  of 
Munster,  Agassiz  and  Bronn,  with  a copy  of  the  figure  of  the  teeth  of  the  Placodus 
Andriani  given  by  Agassiz.  Not  haring  then  had  the  opportunity  of  examining  any 
original  specimens  of  this  singular  extinct  animal,  I adopted,  the  more  readily,  the  cur- 
rent opinion  as  to  its  nature,  from  the  statement  by  Agassiz,  that  the  teeth  resembled 
in  microscopic  structure  those  of  other  Pycnodont  generaf . 
In  1843  Count  Munster  published  a description  and  figure  of  a considerable  part  of 
the  facial  division  of  the  skull  of  a Placodus  from  the  Muschelkalk  of  Bapeuth,  on 
which  he  founded  a distinct  species,  under  the  name  of  Placodus  7'0stratus%  (Plate  XI. 
fig.  4).  This  specimen  had  the  upper  part  of  the  cranium  imbedded  and  the  palatal 
surface  exposed,  showing  the  marginal  teeth  and  the  palatal  teeth.  The  latter  are  six 
in  number,  three  on  each  side  (ib.  e,f,  g)^  in  two  almost  symmetrical  series,  and  demon- 
strate the  absence  of  any  median  row  of  vomerine  teeth,  such  as  exists  in  Gyrodiis  and 
some  other  unequivocal  pycnodont  fishes.  The  figure  of  the  skull  indicates  the  presence 
of  zygomatic  arches,  with  a curvature  and  span  very  difficult  to  reconcile  with  the  known 
modifications  of  the  plan  of  cranial  structure  proper  to  the  class  of  Fishes.  But  it  has 
been  only  very  recently  that  such  specimens  of  the  rare  and  seemingly  peculiarly 
German  triassic  fossil  have  come  under  my  observation,  and  enabled  me  to  settle  the 
doubts  which  Count  Munster’s  figure  of  Placodus  rostratus  first  suggested. 
In  the  meanwhile  the  essay  by  Herman  von  Meyer,  entitled  “ Fossile  Fische  aus  dem 
Muschelkalk  von  Jena,  Querfurt  und  Esperstadt,”  appeared,  in  the  Part  (Fiinfte  Liefe- 
rung)  of  his  ‘ Palseontographica  ’ which  was  published  in  1849.  In  this  essay  neAv 
localities  of  the  Placodus  are  made  known,  e.  g.  the  Terebratulite  limestone  (Terebratu- 
liten  kalk)  of  Zwetzen.  The  prehensile  modification  of  the  crown  of  the  anterior  teeth 
of  Placodus  gigas  is  well  illustrated  § ; the  distinct  covering  of  a clear  enamel-like  sub- 
stance on  the  crown  of  the  tooth  is  mentioned  ||  ; but  no  suspicion  seems  to  have  crossed 
the  mind  of  this  acute  and  indefatigable  palaeontologist  of  any  error  in  the  ascription 
of  Placodus  to  the  Pycnodont  family  of  Fishes. 
In  the  month  of  October  last  (1857)  some  fossils  from  German  triassic  formations 
were  offered  for  sale  to  the  British  Museum,  including  specimens  of  Placodus  from  the 
*'  Band  i.  p.  138. 
t “ La  structure  microscopique  des  dents  est  la  meine  que  chez  les  autres  genres,  en  sorte  que  je  ne  crois 
pas  me  tromper  en  pla9ant  ce  genre  aux  confines  de  la  famille  des  Pycnodontes.” — Agassiz,  tom.  cit.  p.  217. 
X Beitrage  zur  Petrifacten-kunde,  4to.  Heft  1843,  p.  123.  fig.  1.  taf.  15. 
§ Palaeontograpliica,  4to.  1849,  tab.  33.  fig.  8. 
II  “ Her  ziemlicli  stark  Schmelz  dieser  Zahne  ist  glatt  und  schwarz,  die  davon  liberdeckte  Zaluisubstanz 
weisslicb,”  p.  198. 
