﻿art. 
  4 
  SCULPTURE 
  OF 
  MUSSEL 
  SHELLS 
  MARSHALL 
  9 
  

  

  species 
  of 
  this 
  genus 
  the 
  radiating 
  threads 
  have 
  been 
  observed, 
  

   though 
  they 
  have 
  not 
  yet 
  been 
  found 
  in 
  some. 
  No 
  doubt 
  they 
  will 
  

   be 
  found 
  in 
  all 
  in 
  the 
  course 
  of 
  time. 
  As 
  might 
  be 
  expected 
  in 
  a 
  

   genus 
  containing 
  so 
  many 
  species 
  and 
  ranging 
  over 
  so 
  large 
  a 
  ter- 
  

   ritory, 
  there 
  is 
  some 
  variation 
  in 
  the 
  character 
  of 
  the 
  microscopic 
  

   striae, 
  but 
  it 
  may 
  be 
  said 
  that 
  in 
  all 
  cases 
  these 
  striae 
  conform 
  to 
  some 
  

   one 
  of 
  the 
  few 
  variations 
  found 
  in 
  the 
  Mutelidae. 
  Four 
  specimens 
  

   have 
  been 
  selected 
  for 
  illustration. 
  Plate 
  2, 
  figure 
  3, 
  represents 
  the 
  

   striae 
  on 
  a 
  typical 
  A. 
  patagonleus 
  from 
  Arroyo 
  Miguelete, 
  Monte- 
  

   video, 
  Uruguay 
  (Cat. 
  No. 
  335746, 
  U.S.N.M.). 
  Plate 
  3, 
  figure 
  3, 
  rep- 
  

   resents 
  the 
  striae 
  on 
  a 
  specimen 
  of 
  the 
  rotund 
  form 
  of 
  the 
  same 
  

   species 
  from 
  the 
  Uruguay 
  River 
  (Cat. 
  No. 
  347885, 
  U.S.N.M.) 
  . 
  In 
  this, 
  

   the 
  striae 
  are 
  unusually 
  clear 
  and 
  cover 
  a 
  large 
  part 
  of 
  the 
  surface. 
  

   Plate 
  3, 
  figure 
  2, 
  represents 
  the 
  threads 
  on 
  a 
  specimen 
  of 
  A. 
  inaequi- 
  

   valvis 
  Lea 
  from 
  Lake 
  Nicaragua, 
  Central 
  America 
  (Cat. 
  No. 
  59873, 
  

   U.S.N.M.). 
  Although 
  the 
  species 
  is 
  a 
  very 
  small 
  one 
  and 
  comes 
  

   from 
  so 
  far 
  north, 
  the 
  striae, 
  of 
  which 
  there 
  are 
  about 
  100 
  to 
  the 
  

   millimeter, 
  are 
  strictly 
  according 
  to 
  type. 
  The 
  cracks 
  and 
  crevices 
  

   of 
  this 
  shell, 
  especially 
  on 
  the 
  posterior 
  dorsal 
  area, 
  are 
  apt 
  to 
  re- 
  

   tain 
  remains 
  of 
  fugacious 
  periostracum, 
  which 
  resembles 
  little 
  pieces 
  

   of 
  onion 
  skin, 
  and 
  in 
  which 
  the 
  striae 
  show 
  very 
  plainly. 
  In 
  the 
  two 
  

   species 
  composing 
  the 
  section 
  Virgula, 
  Anodontites 
  (Virgula) 
  ensi- 
  

   f 
  ononis 
  Spix 
  and 
  A. 
  (F.) 
  falsus 
  Simpson, 
  so 
  far 
  no 
  radiating 
  striae 
  

   have 
  been 
  observed. 
  As 
  but 
  five 
  specimens 
  were 
  available 
  for 
  ex- 
  

   amination, 
  it 
  will 
  be 
  well 
  to 
  wait 
  until 
  additional 
  material 
  is 
  studied 
  

   before 
  coming 
  to 
  any 
  definite 
  conclusions 
  as 
  to 
  this 
  group. 
  Because 
  

   of 
  their 
  great 
  length 
  they 
  look 
  unlike 
  other 
  Anodontites. 
  

  

  In 
  the 
  series 
  which 
  Simpson 
  arranges 
  as 
  the 
  " 
  Group 
  of 
  Anodon- 
  

   tites 
  crispatus 
  " 
  twelve 
  of 
  the 
  thirteen 
  species 
  have 
  been 
  examined 
  

   and 
  all 
  of 
  them 
  show 
  the 
  radiating 
  strise. 
  In 
  all, 
  the 
  threads 
  were 
  

   easy 
  to 
  find, 
  were 
  well 
  developed, 
  and 
  were 
  distinctly 
  of 
  the 
  Mutelid 
  

   type. 
  In 
  this 
  group 
  all 
  the 
  species 
  have 
  the 
  peculiarly 
  puckered, 
  

   radiating 
  impressed 
  lines, 
  and 
  drooping 
  concentric 
  folds 
  which 
  I 
  

   have 
  likened 
  to 
  festooned 
  drapery 
  and 
  which 
  Ortmann 
  describes 
  by 
  

   the 
  adjective 
  " 
  scalariform." 
  Some 
  of 
  the 
  species 
  are 
  rather 
  rough, 
  

   such 
  as 
  A. 
  crispatus; 
  others 
  are 
  highly 
  polished, 
  such 
  as 
  A. 
  strebi 
  li 
  

   Lea 
  and 
  A. 
  holtonis 
  Lea. 
  In 
  this 
  group, 
  as 
  in 
  most 
  other 
  Anodon- 
  

   tites, 
  the 
  striae 
  are 
  most 
  easily 
  found 
  on 
  some 
  part 
  of 
  the 
  posterior 
  

   dorsal 
  area, 
  but 
  it 
  is 
  not 
  unusual 
  to 
  find 
  them 
  on 
  the 
  disk 
  of 
  the 
  shell 
  

   in 
  spots 
  covered 
  with 
  the 
  puckered 
  radiating 
  impressed 
  lines. 
  Plate 
  

   1, 
  figure 
  1, 
  represents 
  the 
  radiating 
  striae 
  of 
  a 
  specimen 
  of 
  Anodon- 
  

   tites 
  crispatus 
  Bruguiere 
  from 
  Venezuela 
  (Cat. 
  No. 
  24020, 
  U.S.N.M.), 
  

   in 
  which 
  there 
  are 
  about 
  90 
  striae 
  to 
  the 
  millimeter. 
  

  

  This 
  was 
  the 
  first 
  species 
  of 
  Anodontites 
  described 
  and 
  is 
  the 
  type 
  

   of 
  the 
  genus. 
  In 
  many 
  details 
  the 
  periostracum 
  of 
  this 
  species 
  re- 
  

  

  