﻿INVEETEBEATES. 
  

  

  353 
  

  

  There 
  is 
  in 
  Heteroschisma 
  in 
  the 
  proper 
  sense 
  of 
  the 
  word, 
  exteriorly 
  

   no 
  oral 
  ridge 
  ; 
  the 
  part 
  representing 
  it, 
  is 
  concealed 
  from 
  view 
  by 
  

   the 
  overlapping 
  limbs. 
  The 
  limbs 
  are 
  formed 
  intei 
  radially 
  into 
  

   high 
  pyramids 
  with 
  steep 
  sides, 
  of 
  which 
  two 
  of 
  the 
  lateral-walls 
  

   form 
  the 
  sides 
  of 
  the 
  radial 
  sinus. 
  The 
  pyramids 
  enclose 
  all 
  but 
  

   the 
  two 
  inner 
  hydrospires, 
  and 
  are, 
  with 
  the 
  exception 
  of 
  these, 
  

   exposed 
  along 
  the 
  sides 
  of 
  the 
  sinus, 
  but 
  neither 
  their 
  slits 
  nor 
  

   their 
  folds 
  connect 
  externally 
  with 
  the 
  oral 
  plates. 
  The 
  pyramids 
  

   produce 
  also 
  important 
  modifications 
  in 
  the 
  form 
  and 
  position 
  of 
  

   the 
  hydrospires 
  ; 
  in 
  Codaster 
  these 
  organs 
  enter 
  the 
  body 
  nearly 
  at 
  

   right-angles, 
  and 
  the 
  walls 
  are 
  placed 
  almost 
  parallel 
  to 
  each 
  other 
  ; 
  

   in 
  Heteroschisma 
  the 
  hydrospires 
  stand 
  obliquely 
  to 
  the 
  sides 
  of 
  the 
  

   sinus, 
  and 
  are 
  much 
  wider 
  at 
  the 
  outer 
  side 
  than 
  at 
  the 
  inner. 
  

   Contrary 
  to 
  the 
  adjoining 
  folds 
  which 
  connect 
  with 
  the 
  slits, 
  these 
  

   increase 
  in 
  width 
  at 
  the 
  inner 
  end. 
  The 
  hydrospires 
  of 
  Hetero- 
  

   schisma 
  are 
  arranged 
  closely 
  around 
  the 
  mouth, 
  while 
  those 
  of 
  

   Codaster 
  are 
  placed 
  away 
  from 
  the 
  mouth. 
  The 
  differences 
  between 
  

   these 
  two 
  genera 
  and 
  the 
  allied 
  Phcenoschisma 
  are 
  well 
  seen 
  in 
  the 
  

   accompanying 
  table 
  : 
  

  

  » 
  

  

  Hydeospikes. 
  

  

  Ambulacba. 
  

  

  Oeals. 
  

  

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  me 
  

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  s 
  

  

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  Heteroschisma 
  includes 
  the 
  following 
  species 
  : 
  Heteroschisma 
  gracile, 
  

   the 
  type 
  of 
  the 
  genus 
  ; 
  Heteroschisma 
  alternatum, 
  and 
  H. 
  alternatum, 
  

   var. 
  elongatum, 
  Wachsmuth, 
  1 
  all 
  from 
  the 
  lower 
  part 
  of 
  the 
  Ham- 
  

   ilton 
  group, 
  Devonian. 
  

  

  i 
  Dr. 
  Knapp, 
  of 
  Louisville, 
  Ky., 
  had 
  the 
  kindness 
  to 
  send 
  me 
  for 
  examination 
  and 
  

   study, 
  his 
  large 
  collection 
  of 
  Louisville 
  Codasters, 
  consisting 
  of 
  nearly 
  40 
  specimens 
  in 
  all 
  

   stages 
  of 
  growth, 
  and 
  embracing 
  at 
  least 
  two 
  well-marked 
  species. 
  Lyon, 
  in 
  describing 
  

   his 
  Codaster 
  allernatus 
  (Owen's 
  Geol. 
  Rep. 
  Vol. 
  III., 
  p. 
  493). 
  evidently 
  took 
  all 
  Louisville 
  

   Blastoids 
  containing 
  hydrospire 
  slits 
  to 
  belong 
  to 
  only 
  one 
  species, 
  and 
  this 
  makes 
  it 
  

   difficult 
  to 
  ascertain 
  now 
  to 
  which 
  of 
  the 
  two 
  forms 
  the 
  name 
  should 
  be 
  applied. 
  His 
  

   generic 
  figure, 
  on 
  PI. 
  V., 
  Fig. 
  3, 
  represents 
  undoubtedly 
  the 
  form 
  which 
  afterwards 
  was 
  

   described 
  by 
  Shumard 
  as 
  Codaster 
  pyramidatus 
  (Acad. 
  Sei., 
  St. 
  Louis. 
  Vol. 
  I., 
  No. 
  2), 
  

   Lyon's 
  figure 
  3 
  b 
  gives 
  a 
  small 
  specimen 
  of 
  the 
  same 
  species; 
  his 
  figure 
  3 
  a, 
  however, 
  is 
  

   not 
  only 
  an 
  entirely 
  different 
  species, 
  but 
  a 
  Heteroschisma. 
  It 
  might 
  appear 
  that 
  tho 
  

   form 
  represented 
  by 
  the 
  first 
  figure 
  should 
  receive 
  Lyon's 
  name, 
  but 
  this 
  would 
  do 
  injus- 
  

   tice 
  to 
  Shumard, 
  the 
  more 
  as 
  Lyon's 
  descriptions 
  are 
  fitted 
  for 
  neither 
  (he 
  one 
  form 
  nor 
  

   the 
  other. 
  It 
  must 
  be 
  further 
  considered 
  that 
  the 
  latter 
  form, 
  which 
  like 
  Meteroschisma 
  

   gracile, 
  has 
  small 
  orals 
  overlapped 
  by 
  the 
  limbs, 
  and 
  large 
  pyramids 
  between 
  the 
  auiliu- 
  

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