﻿102 
  Messrs. 
  H. 
  J. 
  Carter 
  and 
  R. 
  Hope 
  on 
  a 
  new 
  

  

  long 
  and 
  of 
  breadth 
  varying 
  from 
  about 
  10 
  to 
  20 
  millim., 
  of 
  

   a 
  dead 
  shell 
  of 
  a 
  small 
  species 
  of 
  Pecten 
  (?) 
  , 
  itself 
  with 
  other 
  

   objects 
  entangled 
  in 
  threads 
  of 
  byssus, 
  and 
  thereby 
  attached 
  

   to 
  a 
  scallop. 
  The 
  sponge 
  was 
  dry 
  when 
  first 
  observed 
  and 
  

   for 
  the 
  most 
  part 
  incrusted 
  with 
  an 
  even 
  layer 
  of 
  very 
  fine 
  

   dirt. 
  The 
  presence 
  of 
  some 
  foraminiferal 
  shells 
  on 
  the 
  sur- 
  

   face 
  of 
  this 
  layer 
  seems 
  to 
  point, 
  though 
  somewhat 
  doubtfully, 
  

   to 
  its 
  having 
  been 
  deposited 
  in 
  the 
  sea 
  ; 
  but 
  I 
  do 
  not 
  think 
  it 
  

   has 
  any 
  organic 
  connexion 
  with 
  the 
  sponge 
  on 
  which 
  it 
  lies, 
  

   interfering 
  very 
  materially 
  with 
  the 
  examination 
  thereof. 
  It 
  

   is, 
  indeed, 
  somewhat 
  uncertain 
  if 
  the 
  sponge 
  extends 
  under 
  

   the 
  whole 
  of 
  the 
  crust 
  ; 
  but 
  wherever 
  this 
  latter 
  has 
  been 
  

   microscopically 
  examined 
  spicules 
  have 
  been 
  found. 
  

  

  In 
  places 
  where 
  this 
  crust 
  is 
  absent, 
  the 
  sponge 
  presents 
  

   the 
  appearance 
  of 
  an 
  exceedingly 
  thin 
  colourless 
  film, 
  closely 
  

   adhering 
  to 
  the 
  ridges 
  and 
  furrows 
  of 
  the 
  shell 
  or 
  connecting 
  

   by 
  a 
  smooth 
  erect 
  veil 
  the 
  projecting 
  teeth 
  or 
  processes 
  with 
  

   which 
  the 
  shell 
  is 
  furnished. 
  Under 
  the 
  dirt-crust 
  the 
  film 
  

   probably 
  lies 
  evenly 
  on 
  the 
  ridges, 
  bridging 
  over 
  the 
  furrows, 
  

   as 
  it 
  also 
  does 
  in 
  places 
  at 
  the 
  edge 
  of 
  the 
  crust. 
  The 
  basal 
  

   film, 
  where 
  it 
  is 
  exposed, 
  bristles 
  with 
  upright, 
  generally 
  soli- 
  

   tary 
  spicules 
  ; 
  probably 
  in 
  this 
  place 
  the 
  sponge 
  was 
  extending 
  

   its 
  borders, 
  for 
  wherever 
  the 
  dermal 
  membrane 
  is 
  well 
  deve- 
  

   loped 
  it 
  appears 
  as 
  a 
  glistening 
  mat 
  of 
  spicules, 
  only 
  slightly 
  

   hispid 
  through 
  the 
  occasional 
  penetration 
  of 
  single 
  upright 
  

   spicules 
  from 
  beneath. 
  

  

  On 
  examination 
  of 
  a 
  preparation 
  under 
  a 
  power 
  of 
  about 
  

   50 
  diameters, 
  the 
  main 
  skeleton 
  is 
  seen 
  to 
  consist 
  of 
  upright 
  

   " 
  scopuliform 
  bundles 
  " 
  of 
  spicules 
  (PI. 
  VI. 
  fig. 
  A, 
  1), 
  as 
  in 
  

   Mr. 
  Carter's 
  description, 
  in 
  this 
  case 
  somewhat 
  sparsely 
  dis- 
  

   tributed 
  and 
  of 
  comparatively 
  small 
  dimensions, 
  and 
  replaced 
  

   in 
  parts 
  by 
  radiating 
  tufts 
  of 
  spicules 
  springing 
  directly 
  from 
  

   the 
  basal 
  membrane. 
  Probably 
  these 
  tufts 
  may 
  be 
  immature 
  

   columns, 
  as 
  pointed 
  out 
  by 
  Dr. 
  Bowerbank 
  in 
  the 
  case 
  of 
  

   Microciona 
  atrosanguinea 
  (Mon. 
  Brit. 
  Spong. 
  vol. 
  ii. 
  p. 
  140). 
  

   In 
  consequence 
  of 
  the 
  slight 
  development 
  of 
  the 
  main 
  com- 
  

   pared 
  with 
  that 
  of 
  the 
  dermal 
  skeleton 
  the 
  dry 
  aspect 
  of 
  the 
  

   sponge 
  is 
  " 
  flat 
  and 
  even," 
  in 
  marked 
  contrast 
  with 
  the 
  

   hispid 
  papillae 
  of 
  M. 
  atrosanguinea 
  and 
  M. 
  armata. 
  

  

  Measurements 
  of 
  the 
  spicules, 
  which 
  differ 
  considerably 
  

   from 
  those 
  of 
  the 
  specimen 
  described 
  by 
  Mr. 
  Carter 
  ('Annals,' 
  

   1874, 
  vol. 
  xiv. 
  p. 
  457), 
  but 
  approach 
  more 
  closely 
  to 
  those 
  of 
  

   another 
  specimen 
  of 
  which 
  he 
  has 
  very 
  kindly 
  sent 
  me 
  a 
  

   preparation 
  * 
  for 
  comparison, 
  are 
  as 
  follows, 
  the 
  diameter 
  

   given 
  being 
  in 
  all 
  cases 
  that 
  of 
  the 
  largest 
  spicules. 
  

  

  * 
  This 
  was 
  found 
  a 
  few 
  years 
  ago 
  growing 
  over 
  the 
  surface 
  of 
  a 
  red 
  

  

  