﻿akt. 
  4 
  SCULPTURE 
  OF 
  MUSSEL. 
  SHELLS 
  MARSHALL 
  5 
  

  

  Genus 
  SPATHA 
  

  

  Plate 
  4, 
  fig. 
  3 
  

  

  • 
  Microscopic 
  radiating 
  threads 
  in 
  this 
  genus 
  are 
  finer 
  than 
  those 
  of 
  

   the 
  South 
  American 
  genera. 
  They 
  are 
  quite 
  clear, 
  though 
  showing 
  

   some 
  tendency 
  to 
  become 
  reticulate. 
  The 
  threads 
  of 
  Spatha 
  wahl- 
  

   bergi, 
  which 
  are 
  supposed 
  to 
  be 
  represented 
  on 
  plate 
  4, 
  figure 
  3, 
  

   are 
  the 
  finest 
  that 
  have 
  been 
  observed 
  in 
  any 
  shell. 
  The 
  striae 
  are 
  

   so 
  fine 
  that 
  a 
  satisfactory 
  photograph 
  could 
  not 
  be 
  obtained. 
  The 
  

   figure 
  shown 
  here 
  is 
  magnified 
  50 
  diameters. 
  Even 
  with 
  a 
  magnifi- 
  

   cation 
  of 
  100 
  diameters 
  a 
  photograph 
  did 
  not 
  show 
  the 
  striae. 
  The 
  

   specimen 
  shows 
  a 
  bloom 
  here 
  and 
  there, 
  and 
  on 
  these 
  spots 
  the 
  striae 
  

   become 
  very 
  striking. 
  It 
  is 
  estimated 
  that 
  there 
  are 
  in 
  the 
  neighbor- 
  

   hood 
  of 
  300 
  striae 
  to 
  the 
  millimeter 
  in 
  this 
  species. 
  In 
  this 
  genus 
  

   the 
  species 
  differ 
  greatly 
  in 
  form, 
  size, 
  degree 
  of 
  polish, 
  and 
  in 
  

   sculpture. 
  It 
  is 
  interesting 
  to 
  note 
  that 
  the 
  striae 
  appear 
  in 
  wahl- 
  

   bergi, 
  which 
  is 
  a 
  very 
  large, 
  quite 
  smooth 
  shell 
  ; 
  in 
  vignoniana, 
  which 
  

   is 
  rather 
  small 
  and 
  extremely 
  roughened 
  with 
  stout 
  ribs; 
  and 
  in 
  

   chaziana, 
  which 
  is 
  a 
  small, 
  highly 
  polished 
  shell. 
  In 
  this 
  genus, 
  

   no 
  matter 
  what 
  the 
  form 
  of 
  the 
  shell 
  may 
  be, 
  whether 
  long 
  or 
  short 
  

   or 
  rounded, 
  the 
  smulus 
  is 
  always 
  triangular, 
  as 
  it 
  should 
  be 
  in 
  Mutelid 
  

   shells. 
  

  

  Genus 
  MUTELA 
  

  

  In 
  this 
  genus 
  the 
  striae 
  are 
  fine 
  like 
  in 
  the 
  genus 
  Spatka, 
  but 
  are 
  

   not 
  so 
  clearly 
  defined. 
  They 
  are 
  more 
  given 
  to 
  reticulating 
  and 
  

   do 
  not 
  have 
  the 
  appearance 
  of 
  threads 
  laid 
  alongside 
  each 
  other. 
  

   They 
  appear 
  like 
  a 
  lot 
  of 
  fibers 
  more 
  or 
  less 
  felted 
  rather 
  than 
  

   spun. 
  It 
  is 
  quite 
  difficult 
  to 
  find 
  spots 
  in 
  which 
  the 
  threads 
  show 
  

   at 
  all. 
  All 
  the 
  species 
  of 
  Mutela 
  have 
  an 
  elongated 
  form 
  — 
  this 
  

   length 
  in 
  proportion 
  to 
  height 
  being 
  especially 
  marked 
  in 
  Mutela 
  

   rostrata. 
  The 
  sinulus 
  in 
  this 
  genus 
  is 
  not 
  equilaterally 
  triangular 
  

   in 
  any 
  of 
  the 
  species, 
  but 
  the 
  triangle 
  is 
  drawn 
  out 
  posteriorly 
  into 
  

   a 
  long 
  point, 
  yet 
  this 
  does 
  not 
  necessarily 
  mean 
  that 
  the 
  sinulus 
  falls 
  

   outside 
  of 
  allowable 
  variation 
  of 
  the 
  Mutelid 
  type, 
  but 
  simply 
  that 
  

   length 
  of 
  shell 
  has 
  affected 
  form 
  of 
  sinulus. 
  No 
  satisfactory 
  figure 
  

   could 
  be 
  obtained 
  in 
  this 
  genus. 
  

  

  Genus 
  CHELIDONOPSIS 
  

  

  But 
  three 
  specimens 
  of 
  this 
  genus, 
  Chelidonopsis 
  hirundo, 
  were 
  

   available 
  for 
  examination. 
  It 
  is 
  a 
  very 
  peculiar 
  shell, 
  highly 
  

   polished 
  and 
  very 
  elongated, 
  and 
  has 
  a 
  sinulus 
  which, 
  like 
  that 
  of 
  

   Mutela, 
  does 
  not 
  exactly 
  conform 
  to 
  the 
  usual 
  type 
  in 
  the 
  Mutelidae. 
  

   Further 
  study 
  with 
  young 
  specimens 
  is 
  necessary 
  to 
  determine 
  the 
  

   facts 
  in 
  this 
  group. 
  

  

  