884 
SIE  P.  G.  EGEETON  OX  CHOXDEOSTEUS, 
and  elaborate  examination  and  comparison  of  those  recent  fishes  most  calculated  to 
throw  light  upon  the  subject,  has  concluded — 1st,  that  the  Ganoidei  form  a well-defined 
order  between  the  true  osseous  fishes  and  the  Selaceans ; and  2ndly,  that  Agassiz’s  Gew 
of  the  position  of  the  Sturgeons  amongst  the  Ganoidei  is  correct.  Professor  Owex  con- 
siders the  Sturgeon  to  be  “ one  of  the  transitional  steps  from  the  cartilaginous  to  the 
osseous  fishes,”  and  adds  the  weight  of  his  testimony  to  the  soundness  of  Professor 
Agassiz’s  views  in  arranging  the  Sturionidse  imder  the  ganoid  order  of  fishes.  The 
conclusions  arrived  at  by  these  distinguished  authorities  resulted  from  the  examination 
and  comparison  of  the  recent  Sturgeons  and  the  recent  and  extinct  Ganoids;  no  evidence 
having  been  then  obtained  of  the  occun’ence  of  the  former  family  in  the  fossil  state. 
The  discovery,  therefore,  of  a representative  of  the  Stuiionidce  in  the  earliest  oohtic 
deposits,  a period  in  which  the  typical  ganoid  fishes  attained  their  maximum  of  nume- 
rical development,  has  a material  bearing  upon  this  subject,  inasmuch  as  it  supplies  the’ 
only  term  of  comparison  wanting  in  the  inquiry.  The  opportunities  which  I have  had 
of  examining  all  the  specimens  hitherto  brought  to  light,  have  enabled  me  to  ascertain 
most  of  the  significant  features  of  the  basic  Sturgeon,  the  descriptions  of  which  I have 
embodied  in  the  foregoing  memoir.  The  results  may  be  briefly  summed  up  as  follows; — 
1st.  That  in  all  essential  particulars,  more  especially  in  the  arrangement  of  the  cranial 
plates  and  the  oral  apparatus,  in  the  persistence  of  the  chorda  dorsabs  and  partial  ossifi- 
cation of  its  peripheral  elements,  the  fossil  Sturgeon  closely  resembled  the  recent  form. 
2nd.  That  in  the  structure  of  the  opercular  and  hyoid  regions,  and  in  the  greater 
extent  to  which  the  ossification  of  the  endoskeleton  had  proceeded,  it  approached  the 
condition  of  these  organs  in  the  ganoid  fishes,  and  constituted  a transitional  form 
between  these  and  the  recent  Sturgeon. 
3rd.  That  its  bulky  form  and  smooth  integuments,  contrasting  so  strongly  with  the 
tapering  body  and  dermal  armour  of  the  Sturgeon,  afibrd  a striking  instance  of  the 
universal  law  of  special  modification  of  organization  for  peculiar  conditions  of  animal 
existence. 
The  Sturgeons  of  our  own  time,  inhabiting  the  bottoms  of  the  estuaries  of  mighty 
rivers,  subject  to  frequent  paroxysmal  inundations,  reqube  not  only  an  external  form 
of  least  resistance,  combined  with  powerful  propulsory  organs,  to  withstand  the  torrents 
to  which  they  must  necessarby  be  exposed  in  procuring  their  daily  subsistence,  but  also 
a defensive  armour  sufficient  to  fortify  their  bodies  agamst  injmy  from  stones  and  other 
detrital  matters  hurried  down  by  the  force  of  the  streams.  The  basic  Sturgeons  enjoyed 
a more  tranquil  existence.  The  evidence  of  the  associated  moUuscan  and  radiate  forms, 
proves  the  marine  character  of  the  waters  they  inhabited ; the  thinly  laminated  beds  of 
shale  and  limestone  from  which  their  remains  are  exhumed,  testify  to  the  tranquil  con- 
dition of  the  sea  in  which  they  lived ; their  smooth  skin,  harmonizing  in  tint  with  the 
muddy  bottom  on  which  they  reclined,  served  to  conceal  them  from  the  predatory 
Saurians  and  larger  fishes  with  which  they  coexisted ; they  requbed  neither  defensive 
armour  nor  locomotive  energy  for  self-preservation  in  the  fulfilment  of  those  special 
