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XXIX.  On  the  Anatomy  of  Clavagella,  Lam.    By  Richard  Owen,  Esq.,  F.R.S.  ^  Z.S., 
Assistant  Conservator  of  the  Museum  of  the  Royal  College  of  Surgeons  in  London. 
Communicated  September  23,  1834. 
The  specimen  of  Clavagella  which  forms  the  subject  of  the  following  description  was 
dredged  up  by  Mr.  Cuming,  and  belongs  to  the  species  which  my  friend  Mr.  Broderip 
has  characterized  and  named  Clavagella  lata. 
The  soft  parts  of  this  specimen  were  placed  in  spirit  by  Mr.  Cuming  soon  after  it 
was  captured,  and  were  thus  transmitted  in  good  state  for  examination  to  this  country. 
They  differ  considerably  from  the  form  which  the  soft  parts  commonly  assume  in  other 
Bivalves,  being,  as  it  were,  aggregated  into  an  irregular  quadrate,  or  transversely  ob- 
long mass,  convex  anteriorly,  compressed  laterally,  and  contracting  towards  the  poste- 
rior end  of  the  body,  which  is  formed  by  the  smooth  rounded  siphon  containing  the 
anal  and  branchial  canals.  The  exterior  layer  of  the  mantle,  which  envelopes  the  soft 
parts,  is  a  thin  lacerable  membrane,  with  two  openings,  one  anterior,  contracted  to  a 
very  small  size,  for  the  passage  of  the  rudimentary  foot,  the  other  posterior,  corre- 
sponding to  the  respiratory  and  excremental  outlets. 
When  the  soft  parts  are  replaced  in  their  natural  position  in  the  clavate  chamber', 
and  exposed  by  the  removal  of  the  outer  layer  of  the  mantle,  they  present  the  appear- 
ance delineated  in  Plate  XXX.  Fig.  11.  Much  less  of  the  organization  of  the  animal 
is  by  this  means  brought  into  view  than  in  most  other  Bivalves,  in  consequence  of  the 
great  development  of  the  muscular  margin  of  the  mantle.  The  true  foot  is  wholly  con- 
cealed, and  only  the  extremities  of  the  labial  appendages  and  a  small  part  of  the  right 
gill  are  seen  protruding  through  the  interval  between  the  anterior  muscles  of  the 
mantle  and  those  which  go  to  form  the  siphons :  a  small  part  of  the  ovary  may  be  seen 
between  the  anterior  and  posterior  adductor  muscles. 
The  relative  position  of  the  animal  of  Clavagella  to  the  rocky  chamber  which  it  in- 
habits is  as  follows.  The  mouth  is  turned  towards  the  closed  end  of  the  chamber 
marked  a,  which  is  consequently  the  anterior  part.  The  heart  and  rectum  are  nearest 
the  side  where  the  valves  are  connected  by  the  ligament  b,  or  the  dorsal  part : 
the  visceral  mass  projects  towards  the  opposite  or  ventral  side  c,  while  the  siphon  ex- 
tends into  the  commencement  of  the  calcareous  tube  d,  which  leads  out  of  the  anal  or 
posterior  part  of  the  chamber.  The  fixed  valve,  which  covers  the  rough  surface  of  the 
porous  rock  or  coral,  like  the  tiling  of  a  chamber  floor,  and  affords  a  smooth  polished 
surface  for  the  support  and  attachment  of  the  animal,  is  the  left  valve  :  the  right  valve 
>  Plate  XXX.  Fig.  8. 
2  N  2 
