274 
MR.  R.  OWEN  ON  THE  ANATOMY  OF  CLAVAGELLA. 
Th€  same  letters  indicate  the  same  parts  in  each  figure. 
a.  Anterior  wall  of  the  chamber. 
h.  Dorsal  wall.    The  letter  is  placed  on  the  hinge  of  the  fixed  valve. 
c.  Ventral  wall. 
d.  Posterior  or  siphonic  outlet. 
e.  Tubular  communications  with  a  neighbouring  cavity,  here  sent  off  from 
the  posterior  part  of  the  mantle, 
e',  e'.  Calcareous  tubes  secreted  by  the  above  processes  and  extending  into  the 
cavities  contiguous  to  the  throat  of  the  tube, 
e".  A  cavity  communicating  with  the  anterior  part  of  the  chamber. 
/'.  Impression  of  the  posterior  adductor  muscle. 
g' .  Impression  of  the  anterior  adductor  muscle. 
A'.  Impression  of  the  pallial  muscle,  or  third  adductor. 
/.  Posterior  or  large  adductor.    (The  single  adductor  of  the  Ostracea,  &c. 
corresponds  to  this.    The  following  are  superadded  in  other  families 
of  Bivalves.) 
g.  The  anterior,  antero-dorsal,  or  smaller  adductor. 
h.  The  pallial  or  antero-ventral  adductor. 
i.  The  convex  muscular  mass  continued  over  the  anterior  part  of  the  body, 
and  reducing  the  rictus  of  the  mantle  to  the  small  slit  * ,  through  which 
a  bristle  is  placed  in  fig.  12.  (This  mass  is  an  inordinate  development 
of  what  forms  the  muscular  margins  of  the  mantle  lobes  in  other 
Bivalves.) 
Tc.  Muscular  fibres  of  the  siphon. 
I.  The  respiratory,  or  ingestive,  siphonic  canal. 
m.  The  anal,  or  egestive,  siphonic  canal;  m'.  (fig.  16.)  its  valve.  (These 
are  indicated  by  bristles  in  fig.  14.) 
n,  n.  The  labial  or  buccal  appendages. 
0.  The  mouth,  exposed  by  dividing  the  superior  labial  process. 
p.  The  oesophagus. 
q.  The  stomach,  showing  the  orifices  of  the  hepatic  ducts. 
r.  The  ccecum. 
s.  The  intestine. 
s'.  The  anus. 
t.  The  gills  :  in  fig.  1 1  the  right  gill  is  seen  partially  protruded  between 
the  muscular  parts  of  the  mantle. 
u,  u.  The  auricles,   v.  the  ventricle,  of  the  heart. 
VK  The  liver  surrounding  the  oesophagus,  the  stomach,  and  part  of  the  intestine, 
a\  Part  of  the  ovary. 
y.  The  foot. 
