﻿150 
  MR. 
  P. 
  A. 
  BATHER 
  ON 
  TRIGODJOCEHSTUS 
  PROM 
  

  

  of 
  the 
  base-line. 
  The 
  presence 
  of 
  this 
  small 
  basal 
  makes 
  the 
  base 
  

   of 
  the 
  triangle 
  very 
  slightly 
  longer 
  than 
  the 
  two 
  other 
  sides, 
  but 
  

   does 
  not 
  otherwise 
  affect 
  the 
  regularity 
  of 
  the 
  figure 
  ; 
  in 
  fact 
  this 
  

   smallest 
  basal 
  is 
  quite 
  invisible 
  when 
  the 
  calyx 
  is 
  viewed 
  directly 
  

   from 
  below. 
  The 
  sides 
  of 
  this 
  triangle 
  are 
  not 
  straight, 
  but 
  sinuous, 
  

   with 
  a 
  depression 
  on 
  either 
  side 
  of 
  a 
  median 
  swelling. 
  The 
  

   large 
  basal 
  aperture 
  of 
  the 
  calycal 
  cavity 
  forms 
  a 
  circle 
  inscribed 
  

   within 
  the 
  triangle. 
  The 
  diameter 
  of 
  this 
  circle 
  is 
  about 
  1 
  mm. 
  ; 
  

   the 
  thickness 
  of 
  the 
  basal 
  triangle 
  at 
  the 
  middle 
  of 
  each 
  side 
  is 
  

   about 
  *2 
  mm. 
  ; 
  the 
  thickness 
  of 
  the 
  basal 
  triangle 
  at 
  the 
  angles 
  is 
  

   about 
  *5 
  mm. 
  Each 
  of 
  the 
  three 
  larger 
  basals 
  therefore, 
  as 
  seen 
  

   from 
  below, 
  forms 
  a 
  triangle 
  with 
  concave 
  base, 
  and 
  sides 
  concave 
  

   in 
  the 
  lower 
  third, 
  convex 
  in 
  the 
  upper 
  two 
  thirds. 
  As 
  seen 
  from 
  

   the 
  side 
  (PI. 
  VI. 
  fig. 
  7) 
  the 
  largest 
  basal 
  is 
  of 
  irregular 
  hexagonal 
  

   outline, 
  and 
  is 
  bisected 
  by 
  a 
  ridge 
  running 
  vertically 
  between 
  its 
  

   extreme 
  adoral 
  and 
  aboral 
  angles 
  : 
  the 
  aboral 
  angle 
  is 
  obtuse, 
  the 
  

   adoral 
  angle 
  is 
  very 
  little 
  less 
  than 
  a 
  right 
  angle 
  ; 
  the 
  sides 
  contain- 
  

   ing 
  these 
  two 
  angles 
  are 
  of 
  nearly 
  equal 
  length, 
  and 
  are 
  clearly 
  

   defined 
  by 
  the 
  basi-radial 
  sutures 
  above, 
  and 
  by 
  the 
  free 
  aboral 
  

   margin 
  of 
  the 
  basal 
  below 
  : 
  the 
  two 
  other 
  sides 
  of 
  the 
  hexagon, 
  

   representing 
  interbasal 
  sutures 
  now 
  invisible, 
  are 
  relatively 
  short, 
  

   about 
  '25 
  mm. 
  The 
  two 
  basals 
  next 
  in 
  size, 
  as 
  seen 
  from 
  the 
  side; 
  

   are 
  pentagonal 
  (PI. 
  VI. 
  fig. 
  7) 
  ; 
  they 
  differ 
  from 
  the 
  largest 
  basal 
  

   in 
  the 
  less-marked 
  character 
  of 
  the 
  vertical 
  median 
  ridge, 
  and 
  in 
  

   the 
  absence 
  of 
  an 
  aboral 
  angle 
  : 
  each 
  joins 
  on 
  to 
  the 
  largest 
  basal 
  

   by 
  one 
  side, 
  while 
  by 
  the 
  other 
  sides 
  they 
  join 
  one 
  another 
  : 
  the 
  

   sutures 
  have 
  disappeared, 
  but 
  their 
  former 
  position 
  is 
  indicated 
  by 
  

   three 
  slight 
  depressions 
  on 
  the 
  edge 
  between 
  the 
  aboral 
  and 
  lateral 
  

   surfaces 
  of 
  the 
  basal 
  ring. 
  The 
  smallest 
  basal 
  (PL 
  VI. 
  figs. 
  2 
  & 
  7) 
  

   is 
  a 
  mere 
  tubercle 
  lying 
  between 
  the 
  second 
  and 
  third 
  basals, 
  and 
  

   forming 
  at 
  this 
  point 
  a 
  minute 
  adoral 
  angle, 
  which 
  resembles, 
  

   in 
  everything 
  except 
  size, 
  the 
  adoral 
  angles 
  of 
  the 
  other 
  basals. 
  

   The 
  outer 
  lateral 
  surface 
  of 
  these 
  basals 
  is 
  ornamented 
  with 
  minute 
  

   granules, 
  irregularly 
  arranged. 
  

  

  The 
  Radials 
  are 
  four 
  in 
  number 
  and 
  are 
  of 
  two 
  sizes. 
  They 
  rest 
  

   between 
  the 
  adoral 
  angles 
  of 
  the 
  four 
  basals, 
  and 
  their 
  lower 
  ends 
  

   are 
  gently 
  curved. 
  The 
  two 
  radials 
  on 
  either 
  side 
  of 
  the 
  largest 
  

   basal 
  (PI. 
  VI. 
  fig. 
  1) 
  are 
  broader 
  than 
  the 
  other 
  two 
  and 
  in 
  a 
  

   horizontal 
  section 
  through 
  the 
  calyx, 
  about 
  halfway 
  up, 
  would 
  form 
  

   two 
  sides 
  of 
  a 
  roughly 
  triangular 
  figure. 
  That 
  on 
  the 
  right 
  is 
  very 
  

   slightly 
  broader 
  than 
  the 
  other. 
  The 
  two 
  other 
  radials, 
  which 
  lie 
  

   on 
  either 
  side 
  of 
  the 
  smallest 
  basal 
  (PI. 
  VI. 
  fig. 
  2), 
  are 
  little 
  more 
  

   than 
  half 
  the 
  breadth 
  of 
  the 
  larger 
  radials 
  ; 
  they 
  lie 
  in 
  one 
  plane, 
  

   and 
  would 
  form, 
  in 
  section, 
  a 
  base 
  to 
  the 
  triangular 
  figure 
  slightly 
  

   longer 
  than 
  either 
  of 
  the 
  two 
  sides. 
  The 
  suture 
  between 
  these 
  

   two 
  smaller 
  radials 
  is 
  obscured 
  by 
  anchylosis. 
  Each 
  of 
  the 
  radials 
  is 
  

   rounded 
  from 
  side 
  to 
  side, 
  so 
  that 
  the 
  sutures 
  lie 
  in 
  grooves, 
  

   which 
  are 
  of 
  varying 
  depth. 
  The 
  interradial 
  groove 
  into 
  which 
  

   the 
  adoral 
  angle 
  of 
  the 
  largest 
  basal 
  projects 
  is 
  by 
  far 
  the 
  most 
  

   marked. 
  The 
  opposite 
  groove, 
  that, 
  namely, 
  into 
  which 
  the 
  

  

  