MR.  R.  OWEN  ON  THE  ANATOMY  OF  THE  BRACHIOPODA. 
A',  h' .  Fig.  16.  The  insertions  of  these  muscles  into  the  opposite  valve. 
i.  i.  The  posterior  pair  of  muscles  of  the  perforate  valve. 
k.  k.  The  fringed  brachia,  or  labial  arms. 
Z.  I.  Their  free  spiral  extremities. 
m.  m.  The  branchial  vessels  ramifying  upon  the  mantle-lobes. 
n.  n.  The  two  systemic  hearts. 
0.  The  mouth. 
p.  The  stomach, 
g.  The  liver, 
r.  The  ova. 
PLATE  XXIII. 
Anatomy  of  Orbicula. 
1.  Orbicula  Cumingii,  Brod.,  natural  size. 
1*.  Orbicula  strigata,  Brod. 
2.  Group  of  Orbicula  lamellosa,  Brod.,  natural  size. 
3.  External  surface  of  the  lower  or  flattened  valve  of  Orbicula  lamellosa. 
4.  Internal  surface  of  the  same. 
a.  a.  The  muscular  impressions. 
b.  The  fissure  through  which  the  pedicle  passes. 
c.  The  central  process,  or  ridge  of  the  perforated  valve. 
5.  The  soft  parts  of  Orbicula  lamellosa,  in  situ,  after  the  removal  of  the  convex 
valve ;  showing  the  ciliated  and  vascular  mantle,  the  shell-muscles  and 
visceral  mass. 
6.  The  soft  parts  of  Orbicula  lamellosa,  exposed  by  the  removal  of  the  flattened 
and  perforated  valve,  showing  a  similarly  organized  mantle-lobe,  and  the 
expanded  base  of  the  pedicle,  or  foot. 
7.  The  soft  parts,  as  in  Fig.  5,  farther  exposed  by  reflecting  the  mantle-lobe. 
The  stomach  and  decussating  visceral  muscles  are  shown  by  the  removal 
of  the  liver  and  ovary, 
8.  The  soft  parts,  as  in  Fig.  6,  similarly  exposed  by  the  reflection  of  the  mantle- 
lobe,  and  the  removal  of  the  liver  and  ovary.  The  whole  course  of  the 
intestinal  canal  is  here  seen. 
9.  The  visceral  mass  and  reflected  portions  of  the  arms,  with  their  spiral  ex- 
tremities, and  the  cavities  in  the  muscular  stem  exposed.  The  alimentary 
canal,  with  the  mouth  and  anus,  and  the  liver  and  ovary,  are  shown. 
10.  A  side  view  of  the  soft  parts,  with  the  mantle-lobes  separated  to  show  the 
anus  just  below  the  bend  pf  the  right  arm,  the  spiral  extremity  of  which 
is  unfolded. 
