AND  ACCOUNT  OF  A  NEW  SPECIES  OF  SEPIOLA. 
79 
with  connecting  folds,  they  are  probably  developed  here  chiefly  to  sheath  the  tentacula. 
The  Octopods  which  have  no  tentacula  have  membranes  extended  between  the  bases  of 
all  their  arms  to  serve  as  organs  of  progressive  motion,  because  they  have  no  other  fins. 
The  form  of  the  two  circular  lips  around  the  mouth,  the  structure  of  the  horny  man- 
dibles, and  the  arrangement  of  the  muscles  which  move  them,  agree  with  those  of  Lo- 
ligo.  The  skin  of  the  head  passes  transparent  over  the  pupil,  presenting  only  a  slight 
looseness  above  the  eye,  which  by  folding  produces  the  appearance  of  an  upper  longi- 
tudinal eye-lid.  The  eyes  are  very  large  and  prominent,  and  with  a  remarkable  sub- 
dorsal aspect.  I  have  often  found  this  animal  broader  across  the  eyes  than  at  any  other 
part  of  the  body.  The  back  part  of  the  head  is  continuous  with  the  dorsal  margin  of 
the  mantle,  where  the  dorsal  lamina  commences,  for  about  a  line  in  breadth,  giving  con- 
siderable support  to  both  parts  of  the  body.  The  free  margin  of  the  mantle,  in  all  the 
specimens  I  have  seen,  has  a  white  band  passing  round  the  orifice  of  the  sac.  It  is  en- 
tirely destitute  of  the  usual  spotted  markings  of  the  surface,  and  it  appears  as  if  the 
spotted  skin  were  forcibly  retracted  to  the  extent  of  half  a  line  around  the  margin, 
and  thus  drew  out  the  white  lining  membrane  of  the  interior  of  the  sac.  The  body  of 
this  animal  is  scarcely  ventricose,  being  generally  as  wide  at  the  upper  margin  of  the 
sac  as  at  its  middle,  and  it  is  suddenly  rounded  and  broad  at  the  base.  It  is  supported 
feebly  along  the  middle  of  the  back  by  a  thin,  short,  tapering  dorsal  lamina,  lodged, 
as  usual,  loosely  in  a  capsule,  without  receiving  any  muscular  insertions.  It  is  broadest 
at  the  upper  end,  where  it  measures  about  half  a  line  in  breadth,  and  tapers  regularly 
to  a  point  as  fine  as  a  hair,  extending  only  aboat  a  third  of  the  length  of  the  mantle'. 
On  removing  the  skin  from  the  place  occupied  by  this  most  minute  dorsal  lamina,  a 
dark  line  is  seen  extending  along  its  course  in  the  back.  The  existence  of  this  short 
dorsal  lamina  in  Sepiola  is  the  only  anatomical  fact  regarding  this  animal  recorded  by 
Cuvier,  Lamarck,  and  other  naturalists,  and  it  forms  a  peculiarity  by  which  it  differs 
from  all  the  known  Loligines  with  which  this  animal  has  been  generally  associated. 
The  two  dorsal  fins"^  are  of  great  size  and  strength,  though  attached  but  loosely  to  the 
back  of  the  mantle  near  the  median  plane.  They  are  attached  obliquely  to  the  trunk, 
so  as  to  strike  the  water  most  readily  backwards  and  downwards  during  the  act  of 
swimming ;  they  have  a  deep  notch  at  their  anterior  point  of  junction  with  the  mantle, 
by  which  they  have  greater  extent  of  motion,  and  they  terminate  in  a  very  thin  semicir- 
cular free  margin.  The  fins  are  supported  by  two  firm  crescentic  cartilaginous  plates,  like 
scapules,  which  play  freely  on  the  outer  surface  of  the  mantle,  and  thus  give  great  extent 
and  effect  to  the  motions  of  these  powerful  dorsal  arms.  An  outer  and  inner  layer  of 
muscles,  in  form  of  minute  white  fasciculi,  are  seen  to  pass  from  the  middle  of  the  dorsal 
part  of  the  mantle  to  be  attached  to  these  cartilaginous  scapula,  and  singularly  resemble 
the  mode  of  attachment  of  the  anterior  extremities  of  Vertebrata.    The  syphon  is  here 
'  Fig.  5.  '  Fig.  5. 
