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XXXV.  On  Chondrosteus,  an  Extinct  Genus  of  the  Sturionidce,  fownd  in  the  Lias 
Formation  at  Lyme  Regis.  By  Sir  Philip  de  Malpas  Grey  Egerton,  Bart.,  M.P., 
F.R.S.,  F.G.S.  (&c. 
Eeceived  April  20, — Bead  May  6,  1858. 
Genus  CHONDKOSTEUS,  Agassiz. 
(Subkingdom  Vertebrata,  Class  Pisces,  Order  Goniolepidoti,  Family  Sturiohid^.) 
Head  covered  with  bony  plates.  Body  short,  deep,  adpressed,  devoid  of  dermal  plates. 
Scapula  and  coracoid  united.  Dorsal  fin  advanced.  Tail  heterocerque.  Fin-rays  for- 
mula: P.  50 ; V.  50;  D.  75;  A.  30;  C.  75.  Endoskeleton  partly  ossified,  partly  carti- 
laginous. 
The  recognition  of  a member  of  the  Sturgeon  family  in  the  fossil  state  is  due  to  Professor 
Agassiz,  whose  quick  perception  detected  in  some  fragmentary  specimens,  found  in  the 
lias  shales  at  Lyme  Eegis,  structural  peculiarities  which  convinced  him  that  this  family 
was  not  unrepresented  in  the  secondary  strata  of  Great  Britain.  The  specimens  first 
discovered  were  portions  of  the  caudal  fin,  and  it  was  from  the  examination  of  these  that 
he  established  the  genus  Chondrosteus,  and  determined  its  affinities  to  the  Sturgeons. 
This  result  is  noticed  at  page  280  of  the  2nd  part  of  the  2nd  volume  of  the  ‘Poissons 
Fossiles,’  but  no  description  is  there  given;  nor  has  the  subject  been  since  alluded  to  by 
the  Professor,  the  engagements  undertaken  in  the  United  States  having  put  a stop  to 
the  preparation  of  the  supplementary  continuation  of  his  great  work  on  which  he  was 
engaged  previous  to  his  departure.  Most  of  the  specimens  subsequently  discovered 
appertain  also  to  the  caudal  region.  The  massive  proportions  of  the  caudal  fin,  the 
strength  of  the  fin-rays,  and  the  thickness  and  hardness  of  the  fulcral  scales  on  the 
upper  lobe,  account  for  the  preservation  of  these  parts  in  more  perfect  condition  than 
others  less  qualified  to  resist  the  destructive  agencies  to  which  they  have  been  exposed. 
Recent  discoveries  have  disclosed  a chain  of  evidence  connecting  these  specimens  with 
others,  some  of  which  were  formerly  assigned  to  the  Sauroid  and  Coelacanthoid  families. 
The  first  link  was  afforded  by  a specimen  which,  in  addition  to  the  lower  lobe  of 
the  caudal  fin,  contained  the  anal  fin;  subsequently  a specimen  came  to  light  having 
the  ventral  fins  superadded  to  the  anal  and  caudal  fins ; and  lastly,  a fine  example  in 
hard  lias,  showing  the  posterior  part  of  the  cranium,  both  pectoral  fins,  both  ventral  fins, 
the  dorsal  fin  and  the  anal  fin  (Plate  LXVII.).  The  snout  and  the  tail  are  deficient. 
The  study  of  this  specimen,  and  more  especially  of  the  scapulocoracoid  arch  and  its 
appendages,  led  to  the  identification  of  many  other  specimens  of  the  anterior  parts 
which  were  not  before  supposed  to  have  belonged  to  this  genus.  The  facts  brought  to 
MDCCCLVIII.  5 X 
