872 
SIE  P.  G.  EGEETON  OX  CHOXDEOSTETJS, 
light  by  these  discoveries,  and  the  more  extended  observations  based  thereupon,  fully 
corroborate  the  conclusion  arrived  at  by  Professor  Agassiz,  that  this  genus,  although 
differing  generically  from  the  Sturgeons  of  the  present  epoch,  belonged,  nevertheless,  to 
the  same  family.  These  facts  I now  proceed  to  particularize  in  detail,  commencing 
with  a general  description  of  the  most  perfect  specimen,  and  proceeding  step  by  step 
through  the  anatomical  characters  displayed  in  the  several  specimens  I have  examined, 
so  far  as  their  state  of  preservation  will  allow. 
The  most  perfect  specimen  yet  discovered  (Plate  LXVII.)  is  contained  in  a nodule  of 
indm’ated  lias.  The  rostral  and  caudal  extremities  are  deficient,  and  it  is  otheiwise  much 
injured  by  the  attempts  to  relieve  it  from  the  matrix  in  which  it  is  imbedded.  Excluding 
what  remains  of  the  head,  and  measuring  Aom  the  articulation  of  the  pectoral  fin  with 
the  scapulocoracoid  arch  to  the  hinder  margin  of  the  anal  fin,  the  length  of  the  trank  is 
15  inches.  The  greatest  vertical  depth  is  immediately  in  front  of  the  dorsal  fin,  where 
it  measures  6 inches.  In  a recent  Sturgeon  having  the  same  longitudinal  dimensions, 
the  greatest  vertical  depth  is  only  3 inches,  or  in  proportion  to  the  length  as  1 to  5,  the 
relative  proportions  in  the  fossil  being  as  2 to  5.  The  comparative  measurements  are 
more  disproportionate  when  applied  to  a restoration  of  the  fossil  genus.  By  selecting 
from  the  numerous  specimens  which  have  been  found,  a tail  of  a size  corresponding 
with  the  other  parts  of  the  individual  under  description,  and  adjusting  it  thereto,  the 
additional  length  obtained  is  9 inches,  making  a total  length  of  24  inches  from  the 
attachment  of  the  pectoral  fin  to  the  extremity  of  the  upper  lobe  of  the  tail.  The 
measurement  of  the  corresponding  part  in  the  recent  Stm-geon  gives  an  increase  of 
inches,  or  a total  length  of  22^  inches ; the  result  being  that  the  proportion  of  depth 
to  length  in  the  fossil  is  as  1 to  4,  and  in  the  recent  fish  as  1 to  7^.  The  vertical  dia- 
meter of  the  fossil  at  the  point  of  fracture  behind  the  anal  fin  is  4^  inches,  the  corre- 
sponding measurement  of  the  recent  fish  is  only  1 inch.  It  will  be  apparent  fr’om  these 
dimensions  that  the  Sturgeon  of  the  lias  differs  from  the  existing  Sturgeons  m ha’^ing  a 
shorter  and  more  bulky  body,  deepest  in  its  middle  portion,  and  contracting  very  gra- 
dually posteriorly  as  far  as  the  anal  fin.  It  is  shown  by  other  specimens  that  the  dimi- 
nution of  bulk  behind  this  point  was  more  rapid  down  to  the  point  whence  the  caudal 
fin  expands.  The  breadth  of  the  body  was  not,  as  it  is  in  the  Stm’geon  of  the  present 
day,  commensurate  with  the  depth ; for  it  is  evident,  from  the  proximity  of  the  pectoral 
and  ventral  fins  of  either  side  to  their  fellows,  that  the  sides  of  the  fish  were  more  flat- 
tened, and  that  the  horizontal  diameter  of  the  body  was  considerably  less  than  the  ver- 
tical one.  However  striking  and  distinctive  these  proportions  may  be,  compared  with 
the  graceful  and  taper  outlines  of  the  recent  Sturgeons,  other  characters  are  afforded  by 
the  structure,  form  and  position  of  the  natatory  organs,  equally  corroboratfr’e  of  generic 
difference. 
The  fins  in  all  the  recent  Sturgeons  are  thus  arranged : — the  ventral  fins  are  situated 
at  the  commencement  of  the  posterior  third  segment  of  the  body ; the  anal  fin  occu- 
pies a median  position  between  these  fins  and  the  lobe  of  the  tail,  whilst  the  dorsal 
