]yni.  HANCOCK  ON  THE  OEGANIZATION  OE  THE  BEACHIOPODA. 
815 
longer  than  in  Waldheimia.  The  last-mentioned  bands,  too,  are  united  across  the 
intestine,  their  posterior  margins  being  continuous  and  free.  And  not  only  these,  but 
the  gastro-parietals  likewise  sustain  the  inner  extremities  of  two  pseudo-hearts,  of  which 
in  this  genus  there  are  four. 
The  alimentary  tube  in  lAnguJa'^  presents  two  or  three  interesting  modifications. 
The  mouth  is  perfectly  similar  to  that  of  Waldheimia.  and  the  oesophagus,  which  is 
somewhat  elongated,  is  at  first  depressed;  but  on  emerging  backwards  from  between 
the  anterior  occlusors,  becomes  compressed.  The  stomach  is  short,  being  almost  lenti- 
cular, and  the  transverse  dorsal  ridge  is  much  produced.  In  front  it  is  slightly  convex, 
where  it  receives  the  oesophagus ; behind  it  is  a little  produced,  and  an  inconspicuous 
constriction  marks  the  commencement  of  the  intestine,  which  running  backwards,  buried 
beneath  the  lobules  of  the  liver,  and  resting  above  the  posterior  adjustor  muscles,  gra- 
dually descends  towards  the  ventral  lobe,  immediately  in  front  of  the  divaricator  muscle. 
This  straight  portion  of  the  intestine  corresponds  to  the  entire  intestine  of  the  articulated 
Brachiopods,  and  it  thus  appears  that  in  Lingula.^  as  well  as  in  them,  the  first  inflection 
of  the  intestinal  tube  is  towards  the  ventral  surface.  From  thence  the  tube  bends  to 
the  left,  and  turning  forw^ards  and  upwards,  forms  two  large  loops  at  the  posterior  por- 
tion of  the  permsceral  chamber ; it  then  advances  along  the  right  side,  and,  dipping 
under  the  dorsal  extremities  of  the  adjustor  muscles  and  the  pseudo-heart,  opens  through 
a nipple-like  anus^  situated  at  the  right  side  of  the  body  between  the  margins  of  the 
mantle.  The  anal  orifice  is  ample,  and  is  very  easily  distinguished ; it  is  placed  con- 
siderably nearer  to  the  dorsal  than  the  ventral  surface.  The  calibre  of  the  alimentary 
canal  does  not  vary  much ; the  stomach  only  being  a little  enlarged.  The  mucous  mem- 
brane is  very  stout  in  the  oesophagus,  stomach,  and  anterior  portion  of  the  intestine. 
In  the  former  it  is  produced  into  very  large,  prominent,  longitudinal  folds,  which  appear 
to  be  continued  into  the  stomach ; but  this  point  could  not  be  clearly  ascertained ; in 
the  anterior  or  straight  portion  of  the  intestine  the  longitudinal  plaits  seem  almost  to 
have  disappeared,  but  very  delicate  transverse  rugae  are  discernible^.  Similar,  though 
still  more  minute,  rugae  are  found  in  the  convolutions,  where  the  lining  membrane  is 
thin.  The  muscular  coat  of  the  intestine  is  w'ell  supplied  with  transverse  fibres. 
The  alimentary  tube  in  lAngula.,  like  that  in  the  articulated  Brachiopods,  is  sheathed 
in  a transparent,  homogeneous  envelope,  from  which  originate  certain  membranous 
bands,  that  pass  to  the  parietes  of  the  perivisceral  chamber.  These  bands  are  the  homo- 
logues  of  those  already  described  in  the  other  forms,  under  the  designations  of  the 
mesentery,  the  gastro-  and  ilio-parietal  bands. 
The  mesentery  in  Lingula  is  in  a very  rudimentary  condition,  it  being  represented 
merely  by  two  narrow  membranous  expansions  stretching  along  the  upper  and  under 
surface  of  the  oesophagus,  from  the  biliary  ducts  to  the  anterior  parietes : the  dorsal 
mesenteric  band  is  prolonged  betw’een  the  anterior  occlusors.  The  gastro-parietal  bands 
pass  from  the  transverse  ridge  of  the  stomach,  one  on  each  side,  to  the  posterior  surface 
> Plates  LXIY.  figs.  3,  4 ; LXV.  figs.  1,  3,  4.  " Plate  LXVI.  fig.  3.  * Plate  LXIV.  figs.  6,  7. 
MDCCCLVIII.  5 0 
