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XXIII.  On  the  Anatomy  of  the  Calyptrseidse.    By  Richard  Owen,  Esq.,  F.Z.S.,  Assist- 
ant Conservator  of  the  Museum  of  the  Royal  College  of  Surgeons  in  London. 
Communicated  February  25;  1834. 
JVLy  friend  Mr.  Broderip  having,  in  the  course  of  his  examination  of  the  shells  of  the 
family  Calyptreeidcs  in  the  collection  of  Mr.  Cuming,  detected  a  series  of  gradations  in 
the  form  and  extent  of  the  internal  shelly  plate,  intermediate  to  those  characterizing  the 
species  which  have  been  proposed  as  types  of  subgenera,  he  requested  me  to  examine 
the  soft  parts,  and  see  whether  a  corresponding  gradation  prevailed  in  any  of  the  or- 
ganic systems,  or  whether  these  presented  differences  sufficiently  marked  or  constant  to 
sanction  the  adoption  of  the  proposed  subgeneric  divisions. 
Mr.  Cuming's  collection  and  that  of  Captain  King  have  afforded  the  necessary  ma- 
terials for  this  investigation  ;  and  although  the  difference  between  Crepipatella,  Less., 
and  Calypeopsis,  Less.,  in  the  extent  of  the  locomotive  and  respiratory  systems  is  con- 
siderable, yet  the  intermediate  or  connecting  species  present  gradations  in  the  structure 
of  these  parts  corresponding  to  those  in  the  form  of  the  shelly  plate,  the  latter  peculiar 
feature  of  this  family  of  Gasteropods  acquiring  magnitude,  for  the  purpose  of  protect- 
ing the  visceral  mass  and  of  isolating  it  from  the  foot,  in  proportion  as  this  part  is 
better  organized  for  extension  and  contraction. 
The  labours  of  Cuvier',  of  M.  Deshayes^,  and  of  M.  Lesson^  have  sufficiently  eluci- 
dated the  general  plan  of  formation  which  pervades  this  family  of  Gasteropods.  Their 
dissections  illustrate  the  structure  of  the  subgenera  Crepidula,  Calyptraa,  and  Crepi- 
patella respectively ;  but  the  soft  parts  of  Calypeopsis,  Less.,  or  Dispotcea  of  Say,  have 
never  been  figured  or  described  ;  and  two  large  specimens  of  a  species  of  this  sub- 
genus*, kindly  presented  to  me  by  Capt.  P.  P.  King,  have  afforded  me  the  means  of 
adding  a  few  particulars  to  the  amount  of  anatomical  knowledge  already  possessed 
with  respect  to  the  CalyptrcBidoe. 
The  internal  shelly  lamina  in  that  form  of  Calyptrcea  which  M.  Lesson  has  distin- 
guished by  the  name  of  Calypeopsis,  is  free  in  the  whole  of  its  circumference,  forming  a 
dehcate  cup-shaped  shell,  adhering  by  the  base  and  nearly  the  whole  of  one  of  the  sides 
to  the  outer  large  limpet-shaped  shell. 
'  Anat.  de  la  Crepidule,  Mem.  des  MoUusques.  -  Ann.  des  Sci.  Nat.,  torn,  iii  p.  338.  pi.  xvn. 
'  Anat.  de  la  Crepipatella  Adolphei,  Zoologie  de  Duperrey,  tom.  ii.  pt.  1.  p.  292. 
*  Calyptrcea  (Dispottea)  Byronensis,  Gray,  Mus.  Brit. 
