﻿^°^' 
  53*] 
  PETALOGKAPTUS 
  AND 
  CEPHALOGKAPIUS. 
  201 
  

  

  Petalogkapttts 
  minok, 
  sp. 
  nov. 
  (PL 
  XIV. 
  figs. 
  17-21.) 
  

  

  ^Diplograptus 
  palmeus, 
  Tornquist, 
  'Structure 
  of 
  some 
  Diprionidae.' 
  

  

  This 
  small 
  species 
  has 
  usually 
  been 
  regarded 
  as 
  merely 
  a 
  young 
  

   stage 
  of 
  P. 
  palmeus 
  (Barr.), 
  or 
  P. 
  palmeus, 
  var. 
  latus 
  (Barr.), 
  but 
  it 
  

   differs 
  from 
  these 
  in 
  many 
  important 
  particulars. 
  

  

  I 
  had 
  noted 
  this 
  form 
  some 
  little 
  time 
  previous 
  to 
  my 
  visit 
  to 
  

   Sweden, 
  but 
  through 
  lack 
  of 
  good 
  material 
  I 
  did 
  not 
  like 
  to 
  venture 
  

   upon 
  its 
  description. 
  While 
  in 
  Sweden 
  I 
  was 
  fortunate 
  enough 
  to 
  

   see 
  several 
  excellent 
  specimens 
  preserved 
  in 
  relief 
  ; 
  and 
  having 
  since 
  

   my 
  return 
  examined 
  some 
  better 
  material 
  obtained 
  from 
  the 
  Moffat 
  

   district, 
  I 
  no 
  longer 
  hesitate 
  to 
  assert 
  that 
  it 
  must 
  be 
  regarded 
  as 
  

   a 
  new 
  species. 
  

  

  Structure 
  of 
  the 
  Proximal 
  End. 
  — 
  The 
  sicula 
  is 
  slender 
  and 
  very 
  

   long. 
  It 
  tapers 
  so 
  finely 
  in 
  an 
  upward 
  direction 
  that 
  in 
  many 
  

   specimens 
  it 
  is 
  exceedingly 
  hard 
  to 
  say 
  where 
  the 
  sicula 
  ends 
  and 
  

   the 
  virgula 
  begins. 
  In 
  some 
  specimens 
  it 
  is 
  certainly 
  ^ 
  inch 
  long, 
  

   but 
  in 
  others 
  it 
  is 
  slightly 
  less 
  ; 
  its 
  apex 
  usually 
  lies 
  on 
  a 
  level 
  with 
  

   the 
  4th 
  theca 
  of 
  the 
  primordial 
  series 
  and 
  half 
  way 
  up 
  the 
  central 
  

   part 
  of 
  the 
  3rd 
  theca 
  of 
  the 
  second 
  series 
  ; 
  it 
  was 
  furnished 
  with 
  an 
  

   apertural 
  spine. 
  

  

  The 
  sicula 
  is 
  completely 
  visible 
  only 
  when 
  the 
  rhabdosoma 
  is 
  

   viewed 
  from 
  the 
  dorsal 
  side. 
  From 
  its 
  base 
  on 
  the 
  left 
  side 
  

   arises 
  the 
  'primordial 
  bud' 
  whence 
  the 
  first 
  theca 
  originates. 
  It 
  

   grows 
  parallel 
  with 
  the 
  sicula 
  for 
  a 
  short 
  distance, 
  and 
  then 
  

   describes 
  a 
  gentle 
  concave 
  curve 
  outwards. 
  It 
  never 
  exceeds 
  

   -jL 
  inch 
  in 
  length, 
  and 
  is 
  commonly 
  rather 
  less. 
  The 
  sicula 
  is 
  

   apparently 
  free 
  on 
  the 
  right 
  side 
  for 
  ^ 
  of 
  its 
  length, 
  but 
  when 
  

   viewed 
  on 
  the 
  reverse 
  side 
  only 
  the 
  sicula-base 
  and 
  a 
  small 
  portion 
  

   of 
  the 
  side 
  are 
  visible, 
  since 
  the 
  rest 
  is 
  concealed 
  by 
  the 
  connecting- 
  

   canal 
  and 
  the 
  initial 
  part 
  of 
  the 
  theca 
  1\ 
  In 
  its 
  earliest 
  stage 
  this 
  

   theca 
  closely 
  follows 
  the 
  outline 
  of 
  the 
  sicula 
  for 
  a 
  short 
  distance. 
  

   This 
  fact 
  is 
  only 
  seen 
  on 
  the 
  reverse 
  side, 
  so 
  that, 
  viewing 
  the 
  

   rhabdosoma 
  from 
  the 
  obverse 
  side, 
  theca 
  l 
  2 
  appears 
  to 
  originate 
  

   at 
  about 
  5 
  way 
  up 
  the 
  sicula, 
  while 
  in 
  reality 
  it 
  has 
  originated 
  

   earlier. 
  This 
  theca 
  is 
  also 
  concavely 
  curved, 
  but 
  the 
  curve 
  is 
  less 
  

   than 
  that 
  described 
  by 
  theca 
  l 
  1 
  ; 
  and 
  therefore 
  the 
  aperture 
  of 
  

   theca 
  l 
  2 
  rises 
  to 
  a 
  greater 
  height 
  than 
  does 
  that 
  of 
  l 
  1 
  , 
  though 
  both 
  

   are 
  of 
  approximately 
  the 
  same 
  length. 
  

  

  The 
  aperture 
  of 
  theca 
  l 
  1 
  is 
  always 
  more 
  than 
  -^ 
  inch 
  above 
  

   the 
  base 
  of 
  the 
  sicula. 
  1 
  It 
  rises 
  to 
  a 
  level 
  of 
  y 
  1 
  ^ 
  inch 
  from 
  the 
  

   sicula-base, 
  and 
  is 
  at 
  a 
  distance 
  of 
  -J* 
  inch 
  from 
  it. 
  

  

  Character 
  of 
  Mature 
  Rhabdosoma. 
  — 
  The 
  rhabdosoma 
  is 
  always 
  

   small 
  ; 
  it 
  is 
  commonly 
  i 
  inch 
  long, 
  but 
  a 
  few 
  specimens 
  have 
  

   been 
  found 
  in 
  which 
  this 
  dimension 
  is 
  slightly 
  exceeded. 
  It 
  is 
  

  

  In 
  all 
  forms 
  of 
  P. 
  palmeus 
  (Barr.), 
  the 
  first 
  thecal 
  aperture 
  is 
  always 
  

  

  Q. 
  J. 
  G. 
  S. 
  No. 
  210. 
  

  

  