﻿190 
  

  

  MISS 
  G. 
  L. 
  ELLES 
  ON 
  THE 
  STJBGENEEA 
  [^ay 
  1897, 
  

  

  first 
  theca 
  of 
  the 
  primordial 
  series 
  with 
  the 
  first 
  of 
  the 
  second 
  series. 
  

   Dr. 
  Holm 
  has 
  used 
  it 
  in 
  this 
  sense. 
  It 
  is 
  completely 
  visible 
  on 
  the 
  

   reverse 
  side 
  of 
  the 
  rhabdosoma. 
  The 
  later 
  that 
  theca 
  l 
  2 
  develops 
  

   from 
  theca 
  l 
  1 
  , 
  the 
  shorter 
  is 
  the 
  connecting-canal. 
  If 
  l 
  2 
  does 
  not 
  

   arise 
  till 
  after 
  theca 
  l 
  1 
  has 
  grown 
  past 
  the 
  apex 
  of 
  the 
  sicula, 
  the 
  

   connecting-canal 
  is 
  practically 
  reduced 
  to 
  nothing. 
  It 
  is 
  generally 
  

  

  Two 
  early 
  stages 
  in 
  the 
  development 
  of 
  Petalograptus 
  folium 
  (His.). 
  

  

  ~Virgv,l<s. 
  

  

  ^ 
  

  

  1 
  

  

  '•-tSiciila 
  . 
  

  

  Primordial 
  

  

  6 
  "a. 
  Apertural 
  

  

  Spine 
  of 
  - 
  

   Sicula.. 
  

  

  [Greatly 
  enlarged.] 
  

  

  indicated 
  by 
  the 
  growth-lines 
  running 
  in 
  a 
  direction 
  different 
  from 
  

   those 
  of 
  thecse 
  l 
  1 
  and 
  l 
  2 
  . 
  

  

  In 
  this 
  species 
  the 
  sicula 
  is 
  never 
  completely 
  enveloped 
  by 
  the 
  

   thecse 
  of 
  the 
  rhabdosoma, 
  even 
  at 
  its 
  apex 
  ; 
  it 
  is 
  visible 
  for 
  its 
  entire 
  

   length 
  on 
  the 
  obverse 
  side. 
  In 
  this 
  position 
  it 
  appears 
  to 
  be 
  free 
  

   on 
  the 
  right 
  side 
  for 
  about 
  § 
  of 
  its 
  length 
  ; 
  after 
  that 
  it 
  occupies 
  a 
  

   position 
  midway 
  between 
  thecae 
  l 
  1 
  and 
  l 
  2 
  . 
  In 
  the 
  reverse 
  aspect 
  

   only 
  the 
  base 
  of 
  the 
  sicula 
  and 
  a 
  very 
  small 
  portion, 
  of 
  the 
  side 
  are 
  

   visible, 
  the 
  rest 
  being 
  here 
  concealed 
  by 
  the 
  connecting-canal 
  and 
  

   by 
  the 
  initial 
  part 
  of 
  the 
  second 
  and 
  subsequent 
  thecse. 
  

  

  The 
  first 
  theca 
  of 
  the 
  primordial 
  series 
  seems 
  to 
  grow 
  both 
  

   upwards 
  and 
  downwards 
  in 
  a 
  manner 
  similar 
  to 
  that 
  described 
  by 
  

   Dr. 
  Wiman 
  as 
  characteristic 
  of 
  the 
  genus 
  Diplogrwptus. 
  The 
  

   downward-growing 
  part 
  in 
  this 
  case 
  extends 
  a 
  little 
  way 
  below 
  the 
  

   base 
  of 
  the 
  sicula. 
  

  

  The 
  first 
  theca 
  of 
  the 
  primordial 
  series 
  is 
  usually 
  rather 
  less 
  than 
  

   three 
  times 
  as 
  long 
  as 
  the 
  sicula. 
  It 
  attains 
  a 
  length 
  just 
  short 
  of 
  

   I 
  inch 
  ; 
  the 
  thecae 
  developed 
  later 
  are 
  slightly 
  longer. 
  All 
  have 
  a. 
  

   distinct 
  concave 
  curvature 
  ; 
  proximally 
  the 
  apertures 
  overlap 
  each 
  

   other 
  from 
  about 
  | 
  width, 
  but 
  distally 
  the 
  overlap 
  is 
  less. 
  The 
  

   width 
  of 
  the 
  rhabdosoma 
  opposite 
  the 
  aperture 
  of 
  the 
  first 
  theca 
  of 
  the 
  

  

  