254 
DR.  WHEELTON  HIND  ON  THE  AFFINITIES  OF  [May  1 893, 
rounded.  Hinge-line  as  long  as  the  greatest  length  of  the  shell. 
Valves  convex,  with  a  blunt  ridge  rising  from  the  superior  border  at 
1  of  its  distance  from  the  anterior  end.  This  ridge  proceeds  down¬ 
wards  at  an  acute  angle  to  the  line  of  obliquity  of  the  shell,  and 
becomes  lost  near  the  inferior  border.  The  anterior  part  of  the  shell 
is  swollen  above,  then  compressed  obliquely,  parallel  to  and  in  front 
of  the  ridge,  expanding  again  into  the  ridge,  and  it  consists  of  rather 
more  than  ^  of  the  whole  shell.  The  posterior  part  is  compressed 
near  the  hinge-line,  more  tumid  and  produced  below.  The  lower 
border  forms  a  U-shaped  curve,  obtusely  rounded. 
Interior . — Three  muscle-scars,  pit-like,  anteriorly ;  one  posterior, 
rounded  near  the  posterior  superior  angle.  Pine  lines  of  growth 
starting  from  the  anterior  extremity  along  the  inferior  border, 
diverging  slightly,  reach  the  ridge  and  become  reflected  upwards  to 
the  inferior  and  posterior  borders.  Periostracum  wrinkled. 
Size. — Greatest  length  diagonal,  25  mm.  (1  inch) ;  length  of 
hinge-line,  9  mm.  (about  |  inch) ;  greatest  width  from  side  to  side, 
8  mm.  (^4  inch). 
Localities. — Xorth  Staffordshire :  Hard  Mine,  Ten-foot,  Moss 
Seams;  Coalbrookdale :  Crawstone;  South  Wales:  Blue  Vein  and 
Darran  Pins. 
Observations. — This  shell  is  easily  distinguished  from  other  groups 
by  its  shape  and  gibbosity.  The  longer  forms  approach  somewhat 
to  A.  triangularis ,  and  the  flatter,  broader  forms  to  A.  quadrata. 
Antheacoptera  quadrata.  (PI.  VIII.  figs.  1-4.) 
Avicula  quadrata,  Sowerby,  Trans.  Geol.  Soc.  ser.  2,  vol.  v.  pt.  3,  pi.  xxxix. 
fig.  17. 
Avicula  quadrata ,  Brown,  ‘  Fossil  Conchology,’  pi.  lxi.**  figs.  27,  28. 
Myalina  quadrata,  Salter,  ‘  Iron  Ores  of  South  Wales,’  pi.  ii.  fig.  16. 
Myalina  meliniformis,  Meek&  Worthen,  ‘Geol.  of  Illinois,’  Palasont.  vol. ii. 
(1866)  pi.  xxvii.  fig.  3. 
Myalina  recurvirostris,  ibid.  pi.  xxvi.  fig.  9  a,  b,  c. 
Specific  Characters. — Shell  compressed,  quadrate  or  U-shaped, 
very  slightly  oblique.  Anterior  side  almost  obsolete.  Posterior  ex¬ 
panded  and  flattened.  Left  valve  slightly  more  convex  than  right 
valve.  Hinge-line  straight,  longer  than  or  as  long  as  the  greatest 
antero-posterior  diameter.  The  lower  border  is  almost  semi¬ 
circular.  Anterior  side  narrow,  compressed,  with  sinuated  margin 
at  the  byssal  notch.  There  is  a  blunt  keel,  which  starts  from  the 
hinge-line  at  ^  of  the  length  from  the  anterior  end  and  passes  down¬ 
wards  and  slightly  backwards,  becoming  soon  expanded  and  lost  on 
the  shell.  The  posterior  end  is  flattened,  expanded  above  its 
posterior  border,  being  almost  straight,  meeting  the  hinge-line  at  an 
obtuse  angle.  Umbones  almost  terminal,  slightly  elevated  above 
the  hinge-line,  and  bent  anteriorly. 
Interior. — Three  anterior  muscle-scars,  pit-like ;  one  posterior, 
which  seems  to  vary  slightly  in  position,  in  one  specimen  being  close  up 
to  the  posterior  superior  angle,  in  another  midway  between  this  angle 
and  the  middle  point  of  the  shell.  Hinge-plate  thickened  and  striated. 
Surface-markings  as  in  previous  species.  Periostracum  wrinkled. 
