852 
ME.  TTAXmOK  ON  THE  OEGANIZATION  OE  THE  BEACHIOPODA. 
seen  through  the  pallial  membrane.  Dr.  Yogt  likewise  points  out  that  the  inner  and 
outer  branches  of  the  so-called  vessels  do  not  appear  to  join  the  trunk-vessel,  but  sup- 
poses that  this  may  be  owing  to  their  having  been  broken  off  on  tearing  up  the  speci- 
men. His  description,  therefore,  clearly  answers  to  that  of  these  white  lines;  he 
appears,  however,  to  have  examined  them  only  from  the  surface.  YTien  the  sinuses 
are  laid  open,  the  white  lines  are  found  to  be  produced  by  a solid,  granular  substance 
adhering  to,  and  standing  up  in  relief  from,  the  outer  walls.  This  substance  is  formed 
apparently  by  a thickening  of  the  epithelial  lining  of  the  sinus,  and  has  probably  some 
function  to  serve  in  connexion  with  the  perivisceral  ramifications,  but  certainly  is  in  no 
way  connected  with  the  blood-circulation. 
The  bladder-shaped  enlargements  (Plate  LXIY.  fig.  3 e,  e)  of  the  lateral  pallial  sinuses, 
alluded  to  by  Dr.  Vogt,  are  nothing  more  than  swellings  occasioned  by  the  contraction 
of  the  pallial  or  marginal  fold,  which,  pressing  upon  the  extremities  of  the  sinuses, 
throws  their  walls  into  wrinkles,  and  hence  this  peculiar  appearance.  But  I have  seen 
nothing  like  the  ramifications  of  the  so-called  vessels  described  by  him  on  the  inner  sur- 
face of  these  bladder-shaped  enlargements,  and  am  inclined  to  conclude  that  he  has  been 
misled  by  some  fragments  of  the  external  epithelium  which  had  been  left  adhering  to 
their  walls. 
Explajstation  of  the  Plates. 
PLATE  LII. 
Fig.  1.  Dorsal  view  of  Waldheimia  australis,  the  shell  having  been  removed: — a,  paUial 
lobe ; h,  body ; c,  peduncle ; d,  great  inner  pallial  sinuses  giving  branches  to 
the  margin ; e,  outer  ditto,  ditto ; f,  genitalia  seen  through  the  pallial  mem- 
brane ; g,  red  matter  of  ditto ; h,  marginal  fold ; i,  setse ; j,  cncumpallial 
vessel ; Jc,  extreme  pallial  margin ; I,  median  fissure,  corresponding  to  longi- 
tudinal plate  in  valve ; m,  depression  occasioned  by  the  hinge-plate  and  the 
bases  of  the  crura ; n,  orifices  for  the  passage  of  the  crui-a ; o,  ridge  formed 
by  the  union  of  the  pallial  margins;  p,  extremities  of  anterior  occlusors; 
g,  ditto  of  posterior  occlusors;  r,  ditto  of  divaricators ; s,  ditto  of  dorsal 
adjustors ; t,  liver  seen  through  the  wall  of  the  body. 
Fig.  2.  Ventral  view  of  the  same ; the  letters  up  to  and  including  k correspond  to  those 
of  fig.  1 : — I,  extremities  of  occlusor  muscles ; m,  ditto  of  divaricators ; n,  ditto 
of  accessory  divaricators ; o,  ditto  of  ventral  adjustors ; p,  ditto  of  peduncular 
muscles ; g,  csecal  extremity  of  intestine,  seen  through  the  wall  of  the  peri- 
visceral chamber ; r,  peduncular  nerves. 
Fig.  3.  Ventral  view  of  variety  of  W.  australis’,  the  letters  correspond  to  those  of  fig.  2. 
The  divaricators  and  their  accessories  are  united. 
Fig.  4.  Internal  view  of  dorsal  valve  of  W.  australis,  showing  the  calcareous  loop: — 
