874 
SIE  P.  a.  EGEETOJT  OX  CHOXDEOSTErS, 
those  supporting  the  hinder  rays  are  the  longest  (Pbie  LXIX.  5-).  Each  metacarpal  bone 
seems  to  have  given  attachment  to  several  of  the  rays.  The  first  ray  is  more  massive 
than  the  succeeding  ones,  and  is  considerably  shorter.  It  appears  to  be  formed  by  the 
coalescence  of  two  or  more  rays,  and  is  subject  to  variations  in  this  respect  consequent, 
it  may  be,  on  the  age  of  the  individual.  The  suiTace  is  corrugated  at  the  base  and 
longitudinally  sulcated  above.  The  succeeding  rays  are  about  fifty  in  number.  The 
anterior  ones  increase  successively  in  length  as  they  recede  from  the  first  or  principal 
ray  as  far  as  the  seventh  or  eighth  ray,  at  which  point  the  maximum  extent  of  the  fin  is 
attained ; and  hence  the  fin-rays  decrease  gradually  to  the  hinder  margin  of  the  fin.  A 
few  of  the  last  rays  lose  their  round  character  and  become  broad  and  inflexible  tri- 
angular plates  attached  by  their  apices,  and  dilated  posteriorly  towards  their  distal 
extremities.  The  principal  rays  continue  single  for  a considerable  distance  from  the 
metacarpus,  without  either  bifurcations  or  transverse  joints;  but  in  the  more  remote 
portions  of  the  organ  dichotomizations  and  joints  are  very  numerous.  In  all  the  other 
fins  the  transverse  articulations  are  continued  to  the  base  of  the  rays.  The  surface  of 
the  pectoral  fin  is  irregularly  beset  with  small  asperities,  a character  which  seiwes  to 
distinguish  a mere  fragment  of  this  fin  from  that  of  any  other  fossil  fish  with  which  I 
am  acquainted.  The  dimensions  of  this  fin,  compared  -with  the  pectoral  fin  of  the 
recent  specimen  already  referred  to  in  the  other  measurements,  are  as  follows : — Eecent 
Sturgeon  3 inches  long  by  I^  wide ; Fossil,  5^  inches  long  by  3^  wide.  The  interval 
between  the  fins  is  3 inches  in  the  recent  and  4 inches  in  the  fossil  fish,  from  the  inner- 
most rays  of  one  fin  to  the  corresponding  rays  of  the  other. 
Ventral  Fins  (Plate  LXVII.  V). — No  traces  of  pubic  bones  have  as  yet  been  found  in 
the  specimens  I have  examined,  but  in  one  where  the  base  of  the  ventral  fin  is  preseiTed, 
the  constituent  fin-rays  are  seen  to  be  attached  to  a series  of  short  styliform  ossicles. 
These  tarso-metatarsal  bones  occur  in  the  recent  Sturgeon  in  a semicartilaginous  con- 
dition, and  in  the  Polypterus,  but  they  are  not  found  in  the  generality  of  recent  osseous 
fishes.  The  ventral  fin,  when  expanded,  forms  a nearly  equilateral  triangle,  the  sides  of 
which  measure  about  2f  inches  each.  It  is  composed  of  more  than  fifty  rays.  These 
increase  gradually  in  length  from  the  first  to  the  twelfth,  yv^hich  is  the  longest.  They 
are  gracefully  curved,  and  are  frequently  subdivided  both  longitudinally  and  trans- 
versely. The  interval  between  the  fins  is  2 inches ; in  the  recent  specimen  it  is 
I inch. 
Dorsal  Fin  (Plate  LXVII.  D). — The  dorsal  fin  is  situated  about  the  middle  of  the 
back,  immediately  above  the  ventral  fins,  extending  over  a space  of  4^  inches,  and 
measuring  3^  inches  in  height.  It  contains  between  seventy  and  eighty  rays.  Of  these 
a few  of  the  anterior  rays  are  short  and  single,  representing  the  fulcral  scales  common 
to  many  genera  of  ganoid  fishes.  They  are  succeeded  by  thick,  jointed  rays,  increasing 
successively  in  height  as  far  as  the  fourteenth,  and  thence  decreasing  gradually  to  the 
posterior  termination  of  the  fin.  The  rays  bifurcate  at  some  distance  from  their  bases, 
and  are  frequently  subdmded  as  they  recede  from  the  body.  The  transverse  joints 
