MR.  R.  OWEN  ON  THE  ANATOMY  OF  THE  BRACHIOPODA. 
147 
that  gallant  and  scientific  officer  Commander  James  C.  Ross,  R.N.^  I  find  that  the 
situation  of  the  ova  in  dried  specimens  when  the  mantle-lobes  adhere  to  the  shell,  would 
be  such  as  Cuvier  has  described. 
It  is  from  the  above-mentioned  materials  that  the  following  account  of  the  anatomy 
of  Terehratula  has  been  derived. 
On  separating  and  removing  the  valves  of  Terehratula,  the  soft  parts  of  the  animal 
appear  as  in  Figg.  5.,  6.,  14.  &  15.  Plate  XXII.  The  arms  and  viscera,  as  in  Lincjula, 
are  inclosed  between  the  lobes  of  the  mantle,  which  are  precisely  adapted  to  the  inner 
surface  of  their  corresponding  valves,  and  are  in  such  close  contact  with  them  as  to 
require  great  care  in  separating  the  valves  from  them.  That  lobe  of  the  mantle  which 
corresponds  to  the  perforated  valve,  is  traversed  longitudinally  by  four  large  vessels 2  ; 
the  opposite  lobe  is  similarly  traversed  by  two  such  vessels^.  These  appearances  were 
constant  in  the  four  specimens  examined.  , 
The  margins  of  the  mantle  are  thickened,  as  is  commonly  observed  in  the  Lamelli- 
branchiate  Bivalves ;  but  which  in  this  case  results  less  from  contraction  than  from  a 
peculiar  structure,  presently  to  be  described.  InLingula  and  Orhicula  the  same  margins 
are  distinctly  and  beautifully  ciliate  ;  but  in  Terehratula  the  marginal  cilia  are  so  minute, 
as  only  to  be  perceptible  by  means  of  a  lens. 
At  the  posterior  part  of  each  of  the  lobes  the  expanded  fleshy  extremities  of  the 
muscles  are  seen  ;  those  which  were  attached  to  the  perforated  valve  being  nearer  the 
hinge  by  their  whole  length,  than  the  anterior  pair  of  the  opposite  valve.  Each  of  the 
oval  muscular  disks  is  composed  of  an  anterior  larger  muscle,  and  a  posterior  smaller 
one.  Through  the  transparent  mantle  may  also  be  seen  the  green-coloured  follicular 
liver  intervening  between  and  surrounding  the  muscles,  and  the  folded  ciliate  arms. 
As  the  visceral  mass  occupies  but  a  small  space  near  the  hinge,  the  lobes  of  the 
mantle  can  be  reflected  to  a  greater  extent  than  in  Lingula.  On  examining  in  this 
way  the  inner  surface  of  the  lobes  of  the  mantle,  another  important  difference  between 
Terehratula  and  Lingula  is  perceived.  In  the  latter  genus  the  branchia  consist,  as 
described  by  Cuvier,  of  narrow  elongated  vascular  productions,  which  are  attached  to 
the  inner  surface  of  the  lobes  of  the  mantle  ;  whereas  in  Terehratula  there  only  appear 
the  venous  trunks  above  mentioned.  These  vessels  I  first  perceived  in  Mr.  Cuming's 
small  specimen,  where  they  were  sufficiently  conspicuous  from  the  outside  of  the 
mantle,  owing  to  their  being  distended  with  coagulated  blood ;  but  on  the  inner  side 
they  are  more  distinctly  seen,  commencing  by  numerous  branches  from  the  margins 
of  the  pallial  lobes,  from  the  union  of  which,  at  about  two  lines  distance  from  the 
'  This  gentleman,  having  learned  from  my  friend  Mr.  Broderip  that  I  was  engaged  in  the  investigation  of  the 
anatomy  of  Terehratula,  submitted  for  my  examination,  in  the  most  liberal  manner,  the  largest  of  the  few 
specimens  which  the  untoward  circumstances  attending  the  late  perilous  expedition  permitted  him  to  bring 
safely  to  this  country.  It  was  fished  up  from  a  depth  of  twenty-two  fathoms  near  Felix  Harbour,  in  lat.  70°  N. 
on  the  east  side  of  Boothia  Peninsula. 
*  m.  m.  Figg.  5.  7.  '  m.  m.  Figg.  6.8. 
VOL.  I.  X 
