﻿12 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL. 
  MUSEUM 
  vol.67 
  

  

  Unuyacu, 
  affluent 
  of 
  the 
  Napo 
  River, 
  Ecuador. 
  The 
  Napo 
  is 
  a 
  

   tributary 
  to 
  the 
  Maranon, 
  which 
  in 
  turn 
  is 
  tributary 
  to 
  the 
  Amazon. 
  

   The 
  description, 
  the 
  figures, 
  and 
  the 
  locality 
  all 
  show 
  that 
  this 
  shell 
  

   is 
  the 
  same 
  species 
  as 
  the 
  one 
  described 
  by 
  Higgins 
  as 
  Mycetopus 
  

   falcatus 
  and 
  called 
  Solenaia 
  falcatus 
  Higgins 
  by 
  Simpson. 
  

  

  Genus 
  DIPLODONTITES 
  

  

  Plate 
  1, 
  fig. 
  3 
  

  

  It 
  was 
  in 
  this 
  genus 
  that 
  the 
  microscopic 
  radiating 
  striae 
  were 
  first 
  

   observed, 
  and 
  they 
  were 
  described 
  and 
  figured 
  in 
  the 
  original 
  descrip- 
  

   tion 
  of 
  the 
  only 
  species, 
  Diplodontites 
  cookei 
  Marshall. 
  4 
  In 
  this 
  

   genus 
  the 
  striae 
  are 
  of 
  unusual 
  importance, 
  as 
  the 
  allocation 
  of 
  the 
  

   genus 
  to 
  its 
  proper 
  family 
  depends 
  upon 
  shell 
  characters 
  and 
  the 
  

   striae 
  afford 
  additional 
  evidence 
  that 
  it 
  belongs 
  in 
  the 
  Mutelidae. 
  In 
  

   this 
  genus 
  they 
  are 
  especially 
  clear 
  and 
  cover 
  nearly 
  the 
  whole 
  sur- 
  

   face 
  of 
  the 
  shell, 
  about 
  90 
  striae 
  to 
  the 
  millimeter. 
  Fugacious 
  perio- 
  

   stracum 
  appears 
  to 
  be 
  lacking, 
  as 
  at 
  best 
  there 
  are 
  only 
  a 
  few 
  traces 
  

   here 
  and 
  there 
  of 
  what 
  may 
  be 
  this 
  kind 
  of 
  material. 
  The 
  genus 
  

   differs 
  from 
  all 
  other 
  Mutelidae 
  in 
  having 
  three 
  cardinal 
  teeth. 
  It 
  

   agrees 
  with 
  them 
  in 
  having 
  no 
  lateral 
  teeth, 
  in 
  the 
  nature 
  of 
  the 
  

   sinlus, 
  and, 
  like 
  most 
  of 
  them, 
  it 
  comes 
  from 
  South 
  America. 
  The 
  

   figure 
  is 
  from 
  a 
  paratype 
  (Cat. 
  No. 
  341473, 
  U.S.N.M.), 
  from 
  a 
  

   tributary 
  of 
  the 
  Rio 
  Colorado 
  in 
  the 
  Province 
  of 
  Santander, 
  Co- 
  

   lombia. 
  

  

  SUMMARY 
  

  

  1. 
  The 
  radiating 
  microscopic 
  threads 
  may 
  be 
  considered 
  a 
  family 
  

   characteristic 
  of 
  the 
  Mutelidae 
  as 
  they 
  appear 
  in 
  all 
  the 
  genera, 
  

   with 
  the 
  possible 
  exception 
  of 
  the 
  genus 
  Mycetopoda. 
  

  

  2. 
  This 
  characteristic, 
  being 
  found 
  in 
  Mutelidae 
  only, 
  is 
  confined 
  

   to 
  naiads 
  inhabiting 
  Africa, 
  South 
  America, 
  Central 
  America, 
  and 
  

   Mexico. 
  

  

  3. 
  Data 
  as 
  to 
  breeding, 
  anatomy, 
  and 
  beak 
  sculpture 
  of 
  the 
  genus 
  

   Diplodontites 
  being 
  lacking, 
  its 
  place 
  in 
  Mutelidae 
  depends 
  upon 
  

   conchological 
  features. 
  The 
  radiating 
  striae 
  add 
  to 
  the 
  number 
  of 
  

   characters 
  which 
  indicate 
  that 
  it 
  belongs 
  in 
  that 
  family. 
  

  

  4. 
  The 
  nature 
  of 
  the 
  periostracum 
  of 
  " 
  Solenaia 
  " 
  falcata 
  Hig- 
  

   gins 
  shows 
  it 
  to 
  be 
  South 
  American, 
  as 
  stated 
  by 
  Higgins, 
  and 
  not 
  

   from 
  southeastern 
  Asia, 
  as 
  supposed 
  by 
  Simpson. 
  It 
  also 
  shows 
  

   that 
  falcata 
  belongs 
  in 
  the 
  family 
  Mutelidae, 
  although 
  to 
  what 
  genus 
  

   remains 
  undecided. 
  

  

  5. 
  The 
  genus 
  Mycetopoda 
  does 
  not 
  strictly 
  conform 
  to 
  the 
  usual 
  

   rule 
  so 
  far 
  as 
  microscopic 
  threads 
  and 
  form 
  of 
  shell 
  are 
  concerned, 
  

   though 
  its 
  sinulus 
  is 
  triangular, 
  like 
  that 
  of 
  other 
  Mutelidae. 
  

  

  4 
  Proc. 
  U. 
  S. 
  Nat. 
  Mus., 
  vol. 
  61, 
  1922. 
  

  

  