﻿of 
  the 
  Graptolitio 
  Gemos 
  Diplograptus. 
  

  

  455 
  

  

  any 
  hydrotkecae 
  and 
  stipes 
  in 
  all 
  stages 
  of 
  development 
  were 
  

   joined. 
  

  

  (6) 
  A 
  most 
  astonishing 
  feature 
  of 
  the 
  compound 
  fronds 
  is 
  

   the 
  position 
  of 
  the 
  siculae 
  at 
  the 
  remote 
  end 
  of 
  the 
  stipes, 
  so 
  

   that 
  the 
  so-called 
  "proximal" 
  sicula-bearing 
  end 
  of 
  the 
  single 
  

   stipes 
  appears 
  in 
  the 
  compound 
  colonial 
  stock 
  as 
  the 
  distal 
  one. 
  

   This 
  is 
  accounted 
  for 
  by 
  the 
  observation 
  that 
  the 
  first 
  hydro- 
  

   thecae 
  of 
  each 
  stipe 
  sprout 
  at 
  the 
  distal, 
  broad 
  end 
  of 
  the 
  

   sicula 
  and 
  that 
  all 
  following 
  hydrothecae 
  make 
  their 
  appearance 
  

   more 
  proximally. 
  The 
  stipe, 
  therefore, 
  is 
  growing 
  backward, 
  

   towards 
  the 
  center, 
  or 
  like 
  a 
  leaf 
  at 
  the 
  base, 
  and 
  the 
  sicula 
  is 
  

   carried 
  to 
  the 
  distal 
  end. 
  

  

  (7) 
  By 
  the 
  possession 
  of 
  a 
  pneumatocyst 
  and 
  the 
  arrange- 
  

   ment 
  of 
  the 
  reproductive 
  organs 
  at 
  the 
  bases 
  of 
  the 
  stipes, 
  the 
  

   colonial 
  stocks 
  of 
  Diplograptus 
  had 
  a 
  general 
  similarity 
  to 
  

   those 
  of 
  certain 
  tiiphonophoroz, 
  while 
  the 
  chitinous 
  structure 
  

   of 
  the 
  hydrothecae 
  and 
  gonangia 
  can 
  be 
  only 
  referred 
  to 
  the 
  

   Sertularians. 
  It 
  thus 
  becomes 
  evident 
  that 
  the 
  genus 
  Diplo- 
  

   graptus, 
  like 
  so 
  many 
  palaeozoic 
  fossils, 
  has 
  the 
  combined 
  prop- 
  

   erties 
  of 
  different 
  groups, 
  thus 
  giving 
  valuable 
  hints 
  in 
  regard 
  

   to 
  the 
  common 
  ancestors 
  of 
  these 
  groups. 
  

  

  EXPLANATION 
  OF 
  FIGURES. 
  

  

  Fig. 
  1. 
  — 
  Diplograptus 
  pristis 
  Hall. 
  Natural 
  sjze. 
  

  

  Fig. 
  2. 
  — 
  Diplograptus 
  pristiniformis 
  Hall. 
  Natural 
  size. 
  

  

  Fig. 
  3. 
  — 
  Diplograptus 
  pristiuiformis 
  Hall. 
  Enlarged 
  six 
  times. 
  

  

  the 
  limestone, 
  a. 
  Pneumatocyst. 
  b. 
  Gonangium. 
  

   Fig. 
  4. 
  — 
  Diplograptus 
  pristis 
  Hall. 
  Enlarged 
  four 
  times. 
  

  

  a. 
  Gonangium 
  filled 
  with 
  siculae. 
  

  

  b. 
  Sicula 
  developing 
  into 
  a 
  stipe. 
  

  

  c. 
  Young 
  stipe 
  with 
  distinct 
  sicula 
  at 
  the 
  distal 
  end. 
  

   Fig. 
  5. 
  — 
  Detached 
  sicula 
  of 
  D 
  pristis 
  Hall 
  with 
  pneumatocyst. 
  

  

  Specimen 
  from 
  

  

  