﻿INVEETEBBATES. 
  363 
  

  

  PENTKEMITIDEA*, 
  D'Orbigny. 
  

  

  1819. 
  D'Orbigny, 
  Prodrome 
  de 
  Palaeont, 
  p. 
  102. 
  

  

  1853. 
  D'Orbigny, 
  Cours 
  Elernentaire, 
  p. 
  139. 
  

  

  1882. 
  Etheridge 
  and 
  Carp., 
  Ann. 
  and 
  Mag, 
  Nat. 
  Hist., 
  p. 
  220. 
  

  

  Pentremitidea 
  Americana, 
  Barris, 
  Nov. 
  Sp. 
  

  

  Body 
  small 
  pyriform, 
  height 
  twice 
  the 
  greatest 
  width, 
  which 
  is 
  

   across 
  the 
  radial 
  lips. 
  Ab-oral 
  side 
  in 
  form 
  of 
  a 
  cone 
  with 
  slightly 
  

   convex 
  sides, 
  triangular 
  at 
  the 
  end,' 
  but 
  gradually 
  assuming 
  a 
  

   strongly 
  marked 
  pentalobate 
  aspect, 
  actinal 
  side 
  of 
  the 
  body 
  equal 
  

   in 
  length 
  to 
  the 
  ab-actinal 
  side 
  ; 
  curving 
  gently 
  in 
  an 
  upward 
  direc- 
  

   tion; 
  broadly 
  truncate 
  and 
  somewhat 
  depressed 
  at 
  the 
  oro-anal 
  re- 
  

   gions. 
  

  

  Basals 
  forming 
  a 
  triangular 
  vace, 
  with 
  rounded 
  angles, 
  and 
  of 
  a 
  

   height 
  greater 
  than 
  the 
  width 
  at 
  the 
  top, 
  upper 
  edges 
  slightly 
  con- 
  

   cave. 
  

  

  Eadials 
  two-thirds 
  the 
  length 
  of 
  the 
  body, 
  a 
  little 
  more 
  sloping 
  

   than 
  the 
  basals; 
  width 
  at 
  basi-radial 
  suture 
  equal 
  to 
  the 
  width 
  of 
  

   the 
  plates 
  at 
  the 
  opposite 
  side. 
  The 
  forks 
  occupy 
  two-thirds 
  the 
  

   length 
  of 
  the 
  plates, 
  are 
  comparatively 
  narrow, 
  and 
  end 
  in 
  a 
  sharp 
  

   point 
  which 
  constitutes 
  the 
  uppermost 
  part 
  of 
  the 
  entire 
  body. 
  The 
  

   sides 
  toward 
  the 
  sinus 
  are 
  elevated 
  and 
  formed 
  into 
  sharp 
  edges 
  

   which 
  stand 
  out 
  at 
  right 
  angles 
  above 
  the 
  ambulacra. 
  Eadial 
  lips 
  

   prominent. 
  

  

  The 
  oral 
  plates 
  are 
  not 
  observed 
  in 
  a 
  side 
  view, 
  they 
  are 
  extremely 
  

   small, 
  and 
  are 
  placed 
  against 
  the 
  tips 
  of 
  two 
  adjoining 
  limbs, 
  within 
  

   the 
  truncation 
  of 
  the 
  peristome, 
  where 
  they 
  form 
  a 
  narrow 
  rim 
  

   around 
  the 
  spiracles. 
  

  

  Ambulacra 
  broadly 
  linear, 
  the 
  lateral 
  sides 
  depressed, 
  and 
  forming 
  

   a 
  deep 
  sulcus 
  ; 
  the 
  inner 
  portions 
  almost 
  on 
  a 
  level 
  with 
  the 
  forked 
  

   plates, 
  except 
  near 
  the 
  mouth, 
  where 
  the 
  whole 
  ambulacrum 
  lies 
  

   deeper 
  than 
  the 
  surrounding 
  plates. 
  

  

  Spiracles 
  ovate, 
  drawn-out 
  in 
  a 
  sharp 
  angle, 
  pointing 
  to 
  and 
  sit- 
  

   uate 
  close 
  to, 
  the 
  mouth. 
  They 
  are 
  placed 
  within 
  the 
  oral 
  plates, 
  

   taking 
  up 
  almost 
  their 
  whole 
  surface, 
  leaving 
  exposed 
  a 
  very 
  narrow 
  

  

  *The 
  genus 
  Pentremitidea 
  differs 
  from 
  Troostocrinus, 
  Slmmard, 
  its 
  nearest 
  allied 
  

   form, 
  in 
  having 
  quite 
  inconspicuous 
  oral 
  plates, 
  always 
  placed 
  within 
  the 
  truncate 
  upper 
  

   face 
  of 
  the 
  body, 
  and 
  only 
  five 
  spiracles; 
  which 
  are 
  strictly 
  interradial: 
  while 
  in 
  Troosto- 
  

   crinus 
  the 
  orals 
  are 
  always 
  visible 
  in 
  a 
  side 
  view 
  of 
  the 
  specimen, 
  and 
  there 
  are 
  ten 
  slit- 
  

   like 
  spiracles 
  along 
  the 
  lateral 
  edge 
  of 
  the 
  ambulacra,, 
  and 
  a 
  separate 
  anal 
  opening. 
  I 
  

   am 
  indebted 
  to 
  Mr. 
  AVachsmuth 
  for 
  the 
  recognition 
  of 
  the 
  above 
  species 
  as 
  Pentremiti- 
  

   dea, 
  and 
  who 
  claims 
  that 
  it 
  is 
  the 
  first 
  one 
  that 
  has 
  been 
  discovered 
  in 
  America. 
  

  

  