253 
DR.  WHEI  LCOX  H1ITD  OX  THE  AFFIXITIES  OP  [May  1 893, 
species  of  this  genus  is  described  by  Williamson  (1886)  in  Phil. 
Mas.  yoI.  ix.  p.  351,  as  Unio  Phittipsii,  and  by  Phillips  in  Mur¬ 
chison's  ‘  Silurian  System,’  p.  88,  as  a  thin  compressed  shell  from 
the  neighbourhood  of  Manchester;  while  Ludwig,  4  Palaeonto- 
graphica,’  yoI.  viii.  pi.  iv.  figs.  13-15,  under  Unio  obtusus,  figures 
one  of  this  genus,  and  in  vol.  x.  pi.  iii.  figures  Anodonta  obstipa, 
CycLas  obuncula ,  Unio  Goldfussanus ,  Anodonta  subparaUela ,  Unio 
Eichwaklanus ,  and  Anodonta  tenera ,  which  may  probably  belong  to 
this  genus. 
AsiPHOXIDA  ( IXTEGROPA  LLIALIA). 
Family  Uxioxidje. 
Genus  Axtheacomya. 
Generic  Characters. — Shell  transverse,  slightly  inequivalve,  in¬ 
equilateral,  the  anterior  end  being  small  and  rounded,  posterior 
produced,  compressed  and  expanded,  generally  truncate.  The 
umbones  are  small,  and  situated  near  the  anterior  end,  very  little 
raised  above  the  hinge-line,  which  is  straight,  long,  and  edentulous, 
and  has  a  narrow  interior  ridge  in  its  posterior  portion.  There  is  a 
blunt  oblique  swelling  which  arises  at  the  umbones,  and,  expanding 
as  it  passes  downward  and  backward,  is  lost  on  the  posterior  part 
of  the  shell.  There  is  what  appears  to  be  a  byssal  furrow,  parallel 
and  anterior  to  the  ridge,  but  it  is  extremely  doubtful  whether  it 
is  not  an  ancestral  relic,  as  I  have  been  unable  to  find  evidence  of  a 
byssal  notch  in  any  of  the  species.  Ligament  external,  as  in 
Anodon.  Many  of  the  species  seem  to  gape  at  both  extremities. 
Interior. — Xacreous  and  smooth,  with  concentric  laminae,  and  fine 
radiating  striae,  most  marked  at  the  pallial  line.  No  trace  of  pallial 
sinus  or  hinge- teeth.  Anterior-adductor  impression  situated  at  the 
extreme  anterior-superior  angle  of  the  shell,  rounded,  with  a 
small  accessory  muscle-scar  above  it.  Posterior-adductor  scar  also 
circular,  just  below  and  in  front  of  the  posterior  end  of  the  hinge¬ 
line. 
Exterior. — Surface  marked  by  fine  concentric  striae  and  lamellae 
of  growth.  Periostracum  wrinkled. 
Remarks. — I  have  replaced  this  genus  in  the  Lnionidae,  as  a 
member  of  which  it  was  originally  described  by  Sowerby  writers 
have  since  that  time  included  it  among  the  Mytilidae  and  Mvacidae. 
It  may  now  he  taken  as  settled  (specimens  having  been  discovered 
showing  the  interior)  that  Antliracornya  does  not  belong  to  the 
former,  though  in  some  forms  the  shape  approaches  somewhat  that 
of  certain  of  the  Modiolae. 
As  to  its  affinity  to  the  Myadae,  it  is  somewhat  difficult  to 
understand  why  so  many  characteristics  of  that  family  were  assumed 
for  Antliracornya.  There  were  a  few  points  only  in  common 
between  the  two,  but  these  were  not  of  generic  value.  The  gaping 
ends,  produced  flattened  posterior,  and  wrinkled  periostracum  are 
possessed  by  members  of  the  Unionidae,  as  well  as  Myacidae,  while 
the  peculiar  V-shaped  marking  on  Anthracomya  senex  resembles  the 
