MR.  R.  OWEN  ON  THE  ANATOMY  OF  CLAVAGELLA. 
273 
The  ovary  1  is  of  a  grey  colour,  forming  a  mass  at  the  dorsal  aspect  of  the  body  above 
the  great  adductor  muscle,  and  extending  ventrad  on  either  side  the  oesophagus  and 
stomach  to  the  opposite  end  of  the  base  of  the  foot. 
All  this  mass  of  intestinal  folds,  hepatic  follicles,  and  ova  was  covered  by  a  thin 
membrane.  The  little  muscular  process,  or  foot-,  which  passes  through  the  anterior 
slit  of  the  mantle  is  but  4  lines  long,  and  half  a  Une  in  breadth  :  its  possible  use  may 
be  to  apply  a  solvent  to  the  rock  in  which  the  chamber  is  excavated. 
The  organization  of  Clavagella,  like  that  of  Aspergillum  described  in  the  '  Reise  von 
Afrik'  of  Dr.  Riippell,  is  thus  seen  to  be  modelled  on  the  type  of  the  Acephalous  Bi- 
valves, and  follows  most  closely,  in  the  variations  from  that  type,  the  modifications 
which  have  been  observed  in  Gastrochcena. 
The  lengthened  worm-like  figure  of  Aspergillum  is  exchanged  in  Clavagella  for  a 
shorter  form,  with  greater  lateral  development :  and  instead  of  the  small  rudimentary 
valves,  which  are  enchased,  as  it  were,  in  the  calcareous  sheath  of  Aspergillum,  we  find 
them  here  largely  developed,  and  one  of  them  always  remaining  at  liberty,  to  be  ap- 
plied by  a  powerful  muscular  apparatus  to  those  ofiices  which  are  essential  to  the 
forcible  expulsion  of  the  fluid  in  the  branchial  cavity,  and  probably  to  assist  in  the  ex- 
cavation of  its  secure  abode. 
PLATE  XXX. 
Fig.  8.  A  portion  of  the  rock  (calcareous  grit),  containing  the  attached  valve  and 
part  of  the  tube  of  Clavagella  lata.  The  chamber  has  been  so  laid  open 
as  to  show  its  greatest  dimensions,  both  in  length  and  breadth. 
9.  Outside  view  of  the  right  or  free  valve  of  the  same  specimen. 
10.  Inside  view  of  the  same,  showing  the  corresponding  muscular  impressions 
to  those  of  the  left  or  fixed  valve. 
11.  Soft  parts  of  Clavagella  lata  viewed  from  the  right  side,  the  dermal  layer  of 
the  mantle,  e,  being  removed. 
12.  Soft  parts  of  Clavagella  lata,  seen  from  the  left  side,  or  that  which  is  in  con- 
tact with  the  fixed  valve.    (The  extremities  of  the  left  labial  appendages 
only  are  here  seen,  no  part  of  the  gill  being  protruded.  A  bristle  is  placed 
in  the  rictus,  or  opening  of  the  mantle.) 
18.  Anterior  view  of  the  soft  parts  of  Clavagella  lata,  after  the  removal  of  the 
outer  or  dermal  layer  of  the  mantle. 
14.  The  same,  with  the  anterior  muscular  mass  reflected  to  show  its  internal 
surface  ;  the  visceral  mass,  composed  of  the  liver  w,  intestine  s,  and 
ovary  x,  from  which  the  foot  y  is  continued. 
15.  Posterior  extremity  of  the  sip/jon. 
16.  The  principal  viscera  displayed. 
'  X.  Figg.  12,  14.  -  y.  Fig.  14. 
