﻿426 
  Eev. 
  T. 
  Hincks 
  on 
  the 
  

  

  gin 
  straight 
  or 
  slightly 
  curved, 
  within 
  it 
  a 
  median 
  denticle, 
  

   below 
  it 
  or 
  upon 
  it 
  an 
  aviculiferous 
  rostrum. 
  Ooecium 
  semi- 
  

   circular 
  or 
  subcrescentic, 
  perforated. 
  

  

  The 
  remarkable 
  delicacy 
  of 
  the 
  material 
  of 
  which 
  the 
  cells 
  

   are 
  composed 
  in 
  all 
  the 
  known 
  species 
  and 
  the 
  total 
  absence 
  

   of 
  strong 
  calcification 
  are 
  characteristic 
  points. 
  The 
  walls 
  are 
  

   thin, 
  with 
  a 
  smooth 
  and 
  shining 
  surface, 
  in 
  some 
  cases 
  tra- 
  

   versed 
  by 
  radiating 
  ribs, 
  and 
  of 
  a 
  whitish 
  colour. 
  The 
  oper- 
  

   culum 
  which 
  closes 
  the 
  orifice 
  partakes 
  of 
  the 
  same 
  delicacy 
  

   of 
  structure 
  and 
  is 
  simply 
  membranous. 
  

  

  RhampJiostomella 
  costata, 
  Lorenz. 
  (PI. 
  XXI. 
  figs. 
  6, 
  7, 
  8.) 
  

  

  Cellepora 
  scabra, 
  Smitt 
  ex 
  parte, 
  Kritisk 
  Fortecliii. 
  &c, 
  iv. 
  p. 
  30, 
  

   pi. 
  xxviii. 
  figs. 
  180-188. 
  

  

  Smitt 
  has 
  ranked 
  under 
  his 
  typical 
  C. 
  scabra 
  the 
  present 
  

   form, 
  which 
  has 
  been 
  rightly 
  treated 
  as 
  a 
  distinct 
  species 
  by 
  

   Lorenz. 
  It 
  is 
  abundant 
  amongst 
  the 
  St. 
  -Lawrence 
  dredgings 
  

   in 
  company 
  with 
  JR. 
  plicata, 
  Smitt, 
  and 
  R. 
  bilaminata, 
  

   Hincks. 
  

  

  In 
  different 
  stages 
  of 
  growth 
  it 
  varies 
  much 
  in 
  appearance, 
  

   as 
  a 
  reference 
  to 
  the 
  figures 
  (PI. 
  XXI. 
  figs. 
  6 
  and 
  8) 
  will 
  

   show. 
  In 
  figure 
  7 
  a 
  group 
  of 
  young 
  marginal 
  zocecia 
  is 
  

   represented, 
  which 
  agrees 
  _ 
  in 
  character 
  with 
  the 
  stage 
  of 
  

   growth 
  figured 
  by 
  Lorenz. 
  A 
  remarkable 
  development 
  of 
  

   the 
  superficial 
  costse 
  (also 
  on 
  the 
  younger 
  cells) 
  is 
  shown 
  in 
  

   figure 
  8. 
  Radiating 
  from 
  the 
  side 
  of 
  the 
  cell 
  they 
  pass 
  

   upward 
  to 
  the 
  summit 
  of 
  the 
  suboral 
  rostrum, 
  the 
  delicate 
  

   white 
  lines 
  forming 
  large 
  areolas 
  round 
  the 
  margin, 
  through 
  

   which 
  the 
  smooth 
  and 
  silvery 
  surface 
  is 
  visible. 
  In 
  this 
  con- 
  

   dition 
  the 
  aspect 
  of 
  the 
  species 
  is 
  completely 
  changed. 
  An 
  

   equally 
  striking 
  change 
  is 
  met 
  with 
  if 
  we 
  pass 
  from 
  the 
  border 
  

   of 
  the 
  colony 
  to 
  the 
  interior. 
  In 
  this 
  region 
  the 
  ocecia, 
  which 
  

   are 
  of 
  large 
  size, 
  are 
  commonly 
  present 
  in 
  great 
  numbers, 
  

   crowding 
  one 
  upon 
  another 
  and 
  completely 
  concealing 
  the 
  

   surface 
  of 
  the 
  cells. 
  In 
  this 
  portion 
  of 
  the 
  colony 
  too 
  

   gigantic 
  avicularia 
  frequently 
  occur 
  in 
  addition 
  to 
  the 
  ordinary 
  

   form, 
  which 
  is 
  usually 
  reduced 
  in 
  size 
  and 
  much 
  less 
  prominent 
  

   than 
  usual, 
  the 
  rostrum 
  being 
  either 
  suppressed 
  in 
  great 
  

   measure 
  or 
  concealed 
  by 
  the 
  larger 
  avicularium 
  which 
  rises 
  

   in 
  front 
  of 
  it. 
  The 
  latter 
  is 
  very 
  tall 
  and 
  massive 
  and 
  of 
  the 
  

   same 
  shape 
  as 
  the 
  smaller 
  form 
  ; 
  it 
  is 
  either 
  suberect 
  or 
  re- 
  

   cumbent. 
  1 
  have 
  not 
  noticed 
  these 
  gigantic 
  avicularia 
  except 
  

   on 
  cells 
  furnished 
  with 
  an 
  ocecium 
  ; 
  but 
  they 
  are 
  not 
  always 
  

   present 
  on 
  these. 
  

  

  A 
  varietal 
  form 
  of 
  this 
  species 
  occurs 
  (var. 
  cristata, 
  PI. 
  

  

  