Vol.  49.] 
ANTHRACOPTERA  AND  ANTHRACOMYA. 
251 
those  described  by  Mr.  It.  Etheridge,  Jun.,  as  Mycilina ,l  and  be  says 
that  bis  specimens  from  the  Cults  Limeworks,  Pitlessie,  Fife,  are 
covered  with  Spirorbis,  a  frequent  occurrence  on  North  Stafford¬ 
shire  specimens.  Sir  J.  W.  Dawson  considers  these  shells  to  he 
embryonic  forms  of  Unio,  to  which  family  he  states  that  the  shell  is 
closely  allied  in  structure  (‘  Acad.  Geol.’  2nd  ed.  p.  202). 
There  is  a  good  deal  of  variation  in  size,  shape,  and  tumidity  of 
the  shells  of  the  different  species  to  which  names  have  been  given,, 
and,  indeed,  it  would  be  easy  to  show  a  series  of  shells  passing 
gradually  from  species  into  species  ;  nevertheless,  there  are  well- 
marked  variations,  which  maybe  regarded  as  being  of  specific  value. 
They  were  evidently  gregarious  in  habit.  Mr.  B,.  Etheridge,  Jun.r 
in  his  4  Palaeozoic  Conchology  of  Scotland,’  quotes  a  specimen  of 
Catamites  surrounded  by  a  number  of  individuals  of  Anthracoptera 
lying  as  if  attached  to  it  by  a  byssus. 
The  specific  forms  of  this  genus  may  be  identified  as  : — 
Anthracoptera  modiolaris.  (PI.  YII.  figs.  1,  1  a,  lb,  3,  4,  5,  6.) 
Avicula  modiolaris,  Sowerby,  Trans.  Geol.  Soc.  ser.  2,  vol.  v.  pt.  3,  pi.  xxxix. 
fig.  18. 
?  Non  Avicula  tenuci,  sic  Brown,  Trans.  Manch.  Geol.  Soc.  vol.  i.  (1841) 
pi.  v.  fig.  23. 
?  Non  id.  Brown,  *  Fossil  Conchology,’  pi.  lxviii.  fig.  9. 
Avicula  modiolaris,  Brown,  ibid.  pi.  lxi.**  figs.  23,  24. 
Mytilus  Wesemaelianus,  Eyck  holt,  ‘  Melanges  paleontologiques  ’  (Mem. 
couronn.  Acad.  roy.  Belg.  t.  xxiv.  1852),  pi.  viii.  figs.  11,  12. 
JDreissenia  infiata ,  B.  Ludwig,  ‘  Palaeontographica,’  vol.  viii.  p.  190,  pi.  lxxi. 
figs.  8-10. 
Dreisscnia  laciniosa,  It.  Ludwig,  ‘  Palseontograpliica,’  vol.  viii.  pi.  v.. 
figs.  15-19. 
Modiola  fwnata.  Brown,  ‘  Fossil  Conchology,’  pi.  lxxi.  figs.  12-13. 
Modiola  wyomingensis,  Lea,  Journ.  Acad.  Nat.  Sci.  Philad.  vol.  ii.  pt.  3, 
1853,  p.  203,  pi.  xx.  fig.  1. 
Myalina  modiolaris,  Salter,  ‘  Iron  Ores  of  South  Wales,’  pi.  ii.  fig.  14. 
?Non  Anthracoptera  Browniana,  Salter,  Mem.  Geol.  Surv.  ‘  Country  round 
Wigan,’  2nd  ed.  p.  37,  fig;.  3,  p.  38,  fig.  3,  a,  b. 
Anthracomya  modiolaris,  Ward,  Trans.  North  Staffs.  Inst.  Min.  &  Mech. 
Eng.  vol.  x.  (1890)  pi.  i.  fig.  13. 
E.  Garner,  ‘  Nat.  Hist,  of  County  of  Stafford,’  pi.  E,  figs.  21,  22,  no  descrip¬ 
tion. 
Specific  Characters. — Shell  triangular,  compressed ;  hinge-line 
nearly  or  quite  as  long  as  the  greatest  length  of  the  shell ;  posterior 
extremity  rounded  or  straight  and  somewhat  emarginate,  meeting 
the  hinge-line  at  an  obtuse  angle.  The  left  valve  is  slightly  more 
convex  than  the  right.  There  is  a  flattened  ridge  starting  at  the 
umbo  passing  backwards  parallel  to  the  hinge-line  at  first,  then 
obliquely  downwards  and  backwards,  becoming  lost  on  the  lower 
part  of  the  posterior  half  of  the  shell.  Beaks  almost  terminal, 
curved  inwards  and  forwards,  not  contiguous,  slightly  elevated 
above  the  hinge-line.  Anterior  part  of  shell  almost  obsolete,  with 
byssal  notch.  Posterior  part  expanded,  flattened,  and  obtusely 
curved  at  the  lower  angle.  Hinge-plate  thick  and  transversely 
striated ;  I  have  counted  as  many  as  ten  striae  on  one  plate. 
1  Ann.  &  Mag.  Nat.  Hist.  ser.  4,  vol.  xv.  (1875)  p.  427,  pi.  xx. 
