﻿202 
  

  

  MISS 
  G. 
  L. 
  ELLES 
  ON 
  THE 
  SUBGENERA 
  [May 
  1 
  897, 
  

  

  concavo-convex, 
  with 
  great 
  convexity 
  on 
  the 
  reverse 
  side. 
  Mature 
  

   forms 
  are 
  oblong, 
  and 
  have 
  a 
  rounded, 
  narrow 
  distal 
  end. 
  The 
  

   maximum 
  width 
  is 
  attained 
  very 
  gradually 
  ; 
  it 
  is 
  never 
  reached 
  till 
  

   halfway 
  up 
  the 
  rhabdosoma, 
  that 
  is, 
  § 
  inch 
  from 
  the 
  proximal 
  end. 
  

   It 
  never 
  exceeds 
  J 
  inch, 
  but 
  is 
  usually 
  about 
  that 
  measurement. 
  

  

  In 
  the 
  longer 
  forms 
  the 
  rhabdosoma 
  remains 
  at 
  the 
  maximum 
  

   width 
  for 
  a 
  very 
  short 
  distance, 
  but 
  more 
  commonly 
  begins 
  at 
  once 
  

   to 
  diminish 
  again. 
  In 
  some 
  specimens, 
  as 
  a 
  result 
  of 
  the 
  extreme 
  

   convexity, 
  the 
  distal 
  end 
  of 
  the 
  reverse 
  aspect 
  is 
  seen 
  to 
  have 
  a 
  

   pointed 
  appearance, 
  but 
  this 
  is 
  not 
  usually 
  the 
  case. 
  

  

  The 
  thecae 
  are 
  alternate 
  ; 
  they 
  are 
  y 
  1 
  ^ 
  inch 
  long 
  and 
  4| 
  times 
  as 
  

   long 
  as 
  wide 
  ; 
  their 
  apertures 
  are 
  very 
  slightly 
  concave, 
  and 
  are 
  

   perpendicular 
  to 
  the 
  long 
  axis 
  of 
  the 
  theca. 
  There 
  are 
  36 
  apertures 
  

   in 
  the 
  space 
  of 
  an 
  inch. 
  There 
  is 
  not 
  much 
  difference 
  in 
  the 
  width 
  

   at 
  the 
  aperture 
  and 
  the 
  width 
  at 
  the 
  initial 
  part. 
  Growth-lines 
  

   parallel 
  to 
  the 
  aperture 
  are 
  often 
  seen. 
  The 
  thecae 
  are 
  inclined 
  to 
  

   a 
  median 
  line 
  at 
  a 
  constant 
  angle 
  of 
  about 
  45°. 
  The 
  amount 
  of 
  

   curvature 
  decreases 
  towards 
  the 
  distal 
  end. 
  On 
  the 
  obverse 
  side 
  

   there 
  are 
  indications 
  of 
  the 
  presence 
  of 
  a 
  septum, 
  but 
  on 
  the 
  reverse 
  

   side 
  in 
  a 
  specimen 
  preserved 
  in 
  relief 
  there 
  is 
  no 
  trace 
  of 
  one, 
  so 
  

   that 
  it 
  must 
  be 
  incomplete. 
  

  

  Tornquist 
  has 
  shown 
  that 
  this 
  is 
  the 
  case. 
  It 
  appears 
  from 
  his 
  

   work 
  that 
  the 
  septum 
  extends 
  half 
  way 
  through 
  the 
  rhabdosoma, 
  

   but 
  it 
  may 
  be 
  still 
  further 
  reduced. 
  

  

  The 
  virgula 
  is 
  conspicuous, 
  and 
  is 
  often 
  distally 
  prolonged. 
  

  

  Measurements 
  oe 
  various 
  Forms. 
  

  

  Spec. 
  

  

  Lugth. 
  

  

  Thecal 
  

  

  length. 
  

  

  No. 
  of 
  

  

  thecce. 
  

  

  Width 
  

   opp.l 
  1 
  . 
  

  

  2 
  1 
  . 
  

  

  3 
  2 
  . 
  

  

  Max. 
  

   width. 
  

  

  L. 
  of 
  

   sicula. 
  

  

  Locality. 
  

  

  *1 
  ... 
  

  

  tV 
  

  

  i 
  

  

  T2" 
  

  

  15 
  

  

  A 
  

  

  B" 
  

  

  5 
  

  

  ¥2" 
  

  

  & 
  

  

  

  Dobb's 
  Linn. 
  

  

  *2 
  ... 
  

  

  tV 
  

  

  A 
  

  

  14 
  

  

  A 
  

  

  -i 
  

  

  b 
  

  

  i 
  

  

  i 
  

  

  B"> 
  

  

  J) 
  5> 
  

  

  *4 
  ... 
  

  

  +* 
  

  

  A 
  

  

  20 
  

  

  A 
  

  

  ... 
  

  

  

  B- 
  

  

  1 
  

  

  >> 
  5» 
  

  

  14 
  ... 
  

  

  +i 
  

  

  T2" 
  

  

  19 
  

  

  +A 
  

  

  — 
  S 
  

  

  "S" 
  

  

  * 
  

  

  

  Skelgill. 
  

  

  16 
  ... 
  

  

  i 
  

  

  1 
  

   T2" 
  

  

  21 
  

  

  ? 
  

  

  1 
  

  

  i 
  

  

  B 
  

  

  + 
  1 
  

  

  

  Dobb's 
  Linn. 
  

  

  23 
  ... 
  

  

  i 
  

  

  1 
  

   T2 
  

  

  18 
  

  

  A 
  

  

  "8 
  

  

  1 
  

   B" 
  

  

  + 
  1 
  

  

  

  ,, 
  „ 
  

  

  25 
  ... 
  

  

  1 
  

  

  A 
  

  

  19 
  

  

  A 
  

  

  — 
  5" 
  

  

  l 
  

   B 
  

  

  I 
  

  

  

  M 
  » 
  

  

  29 
  ... 
  

  

  1 
  

  

  A 
  

  

  18 
  

  

  +tV 
  

  

  +A 
  

  

  — 
  ¥ 
  

  

  i 
  

  

  

  Skelgill. 
  

  

  A 
  

  

  A 
  

  

  T2~ 
  

  

  19 
  

  

  A 
  

  

  

  

  B 
  

  

  B 
  

  

  Tommai'p. 
  

  

  I 
  have 
  also 
  taken 
  measurements 
  of 
  a 
  number 
  of 
  species 
  of 
  all 
  

   ages, 
  and 
  the 
  following 
  table 
  shows 
  the 
  relation 
  between 
  the 
  

   number 
  of 
  thecae 
  and 
  the 
  length 
  : 
  — 
  

  

  