804 
ME.  TTAXmCTC  ON  THE  OEGANIZATIOX  OE  THE  BEACHIOPODA. 
as  if  it  were  necessary  to  avoid  disturbing  the  internal  parts  by  a too  extensive  action 
even  in  this  direction. 
Now,  the  organization  of  Lingula  is  so  similar  to  that  of  the  TerehmtulidcB  as  to  make 
it  difficult  of  belief  that  all  this  precaution,  to  prevent  the  displacement  of  the  valves, 
should  be  necessary  in  the  one  case,  and  that  in  the  other  a special  apparatus  should  be 
provided  to  bring  it  about.  As  Lingula  is  deprived  of  a hinge,  teeth,  and  sockets,  should 
we  not  rather  expect  to  find  some  especial  means  provided  to  compensate  for  such  im- 
portant deficiencies'?  And  do  we  not  see  in  the  large  development  and  comphcated 
arrangement  of  these  muscles  such  compensation  ? This  can  hardly  be  doubted ; and  in 
corroboration  of  this  opinion  it  may  be  stated,  that  Mr.  Baeeett,  who  has  had  the 
opportunity  of  observing  Crania  alive,  states  that  it  opens  the  valves  “ by  mo'sing  upon 
the  straight  side  as  on  a hinge  without  sliding  the  valve*.”  This  would  seem  almost 
conclusive. 
The  homologues  of  the  adjustor  muscles  cannot  be  determined  with  any  great  degree 
of  confidence,  though  it  would  seem  probable  that  they  represent  the  muscles  so  named 
in  the  articulated  Brachiopods.  From  their  posterior  position  this  might  perhaps  be 
inferred,  and  the  relation  of  the  ventral  terminations  of  the  external  adjustors  to  those 
of  the  posterior  occlusors,  is  very  similar  to  the  relation  of  the  ventral  adjustors  to  the 
terminations  of  the  occlusors  in  Waldheimia.  It  would  therefore  seem  likely  that  the 
external  and  central  adjustors  are  the  equivalents  of  the  ventral  adjustors  of  that  genus. 
It  does  not  signify  much  that  in  Lingula  these  muscles  are  dhided  into  two  pams ; for 
we  have  seen  in  Waldheimia  the  liability  of  the  muscles  to  become  double.  If  this 
determination  be  correct,  then  the  posterior  occlusors  will  be  homologous  with  the  dorsal 
adjustors  of  the  articulated  group.  Mr.  Woodwaed  states,  in  his  excellent  ManuaP,  that 
some  of  these  muscles  in  Liscina  are  probably  inserted  into  the  peduncle,  and  if  so  the 
likelihood  of  this  view  of  their  homology  would  be  greatly  enhanced.  -It  is  therefore 
most  desirable  that  the  muscular  system  of  this  genus  should  be  fully  investigated. 
Before  describing  the  peduncular  muscle  it  is  necessary  to  examine  the  pedimcle  itself. 
This  is  enormously  developed ; in  one  of  the  specimens  dissected  it  was  upwards  of  9^ 
inches  long;  it  is  stout  at  the  upper  extremity ^ but  suddenly  contracts  at  its  junction 
with  the  valve ; below  it  tapers  considerably.  On  making  a transverse  section^,  it  is 
found  to  be  cylindrical  and  a little  flattened,  with  the  waUs  formed  of  two  thick  con- 
centric layers,  as  described  by  Dr.  C.  Vogt  in  his  paper  on  the  Anatomy  of  Lingula^. 
The  external  layer  is  homogeneous,  semi-pellucid,  yellowish,  and  horn-hke ; the  mner 
is  opake,  of  a yellow  colour,  and  is  composed  of  longitudinal  muscular  fibres.  This 
muscular  cylinder  extends  from  end  to  end,  and  is  rather  abruptly  constricted  as  it 
approaches  the  ventral  valve  and  is  transformed  into  the  peduncidar  muscle ; the  central 
channel  appears  to  be  continued  through  the  muscle,  and  is  brought  into  commimicatioii 
* Ann.  and  Mag.  of  Nat.  Hist.  vol.  xvi.  p.  257, 1855.  " Manual  of  the  MoUusca,  p.  237, 1851. 
" Plates  LXVI.  figs.  6,  7 ; LXII.  fig.  3.  ^ Plate  EXIT.  fig.  10. 
“ Anatomie  de  la  Lingula  anatina,"  Nouv.  Mem.  Soc.  Helv.  vol.  vii,  Neuchatel,  18-15,  Ito.  plates  1 and  2. 
