263  DE.  WHEELTON  HIXD  ON  THE  AFFINITIES  OF  [May  1 89  3, 
obsolete  diagonal  swelling  crosses  the  shell  obliquely  from  the 
umhones. 
Interior. — Smooth.  Pallial  line  simple.  Anterior-adductor  scar 
at  the  superior-anterior  angle  ;  posterior  large,  hemispherical,  at  the 
upper  part  of  the  posterior  end. 
Exterior. — Surface  marked  with  fine  concentric  lines,  parallel  for 
most  part  of  the  way  to  the  inferior  border. 
Size. — Antero-posterior  measurement,  25  mm.  (1  inch)  ;  dorso- 
ventral,  12  mm.  inch) ;  from  side  to  side,  8  mm.  (^-1  inch). 
llemarlcs. — This  shell  is  somewhat  rare.  It  is  differentiated  from 
other  species  by  its  oblong  rectangular  form,  and  obsolete  anterior 
end.  I  believe  this  shell  is  similar  to  that  described  and  figured  by 
Meek  and  Worthen  in  the  ‘  Palaeontology  of  Illinois.’  They  referred 
their  shell  to  a  Permian  species  (King)  on  account  of  a  few  radiating 
lines  on  the  posterior  surface,  a  kind  of  ornament  which  also  obtains 
in  Anthrctcomya ;  and  describe  the  groove  in  casts,  on  each  side  at 
the  posterior  end  of  the  hinge-line,  as  impressions  of  long  lateral 
teeth,  instead  of  as  an  expansion  of  the  articulating  plate.  It  is, 
however,  impossible  to  speak  positively  without  handling  the 
American  specimens. 
Locality. — Hard  Mine  Seam,  North  Staffordshire. 
Anthkacomya  angusta,  sp.  nov.,  Wheelton  Hind.  (PI.  X.  fig.  15.) 
Specific  Characters. —  Shell  very  transversely  elongated,  narrow. 
Hinge-line  straight,  nearly  as  long  as  the  shell,  not  raised  posteriorly. 
Umbones  small,  obtuse,  very  slightly  raised  above  the  hinge-line, 
situated  about  J  length  of  the  shell  from  the  anterior  end. 
The  inferior  border  is  straight,  being  broadly  grooved  for  the  byssal 
sinus.  Anterior  end  obsolete,  tumid  ;  posterior  end  elongated  and 
flattened.  An  obtuse  angular  ridge  extends  from  the  umbones,  be¬ 
coming  lost  on  the  posterior  part  of  the  shell,  and  there  is  a  broad 
sinus  just  anterior  to  it.  Posterior  border  bluntly  truncated. 
Interior  unknown. 
Exterior. — Surface  ornamented  with  fine  concentric  lines  parallel 
to  the  lower  border,  which  become  strongly  reflected  upward  over 
the  posterior  part  of  the  shell  towards  the  superior  border.  Peri- 
ostracum  very  strongly  wrinkled. 
Size. — Antero-posterior  measurement,  11  mm.  (about  j-  inch); 
dorso-ventral,  6  mm.  (about  4-  inch). 
llemarlcs. — I  know  of  only  one  specimen,  which  is  in  my  own 
collection.  It  is  distinguished  from  other  species  by  its  narrow, 
elongated  form,  and  by  its  surface-markings. 
Locality. — Hard  Mine  Seam,  Buck  nail,  North  Staffordshire. 
Antheacomya  subcentbalis.  (PI.  X.  figs.  30  and  30  a.) 
Salter,  Geol.  Surv.  Mem.,  ‘  Iron  Ores  of  South  Wales,’  pi.  ii.  figs.  9  and  9  a, 
p.  231. 
Specific  Characters.— Transversely  oblong,  convex.  Anterior  end 
rounded,  tumid,  somewhat  prominent.  Posterior  end  bluntly 
