﻿8 
  JUHLIN-DANNFELT, 
  ON 
  THE 
  DIATOMS 
  OF 
  THE 
  BALTIC 
  SEA. 
  

  

  Por 
  the 
  determination 
  of 
  the 
  . 
  more 
  difficult 
  species 
  

   I 
  Beeded 
  a 
  microscope 
  of 
  high 
  magnifying 
  power, 
  and, 
  

   througli 
  the 
  kindness 
  of 
  Profs. 
  Th. 
  Fries 
  of 
  Upsala 
  and 
  S. 
  O. 
  

   LiNDBEEG 
  of 
  Helsingfors, 
  I 
  have 
  had 
  the 
  opportunity 
  of 
  using 
  

   the 
  excellent 
  microscopes 
  belonging 
  to 
  the 
  institutions 
  under 
  

   their 
  superintendence, 
  and 
  I 
  take 
  here 
  an 
  opportunity 
  of 
  

   bringing 
  them 
  my 
  best 
  thanks. 
  Last 
  but 
  not 
  least 
  I 
  am 
  in- 
  

   debted 
  to 
  our 
  renowned 
  diatomist, 
  Prof. 
  P. 
  T. 
  Cleye, 
  for 
  

   the 
  untiring 
  benevolence 
  with 
  which 
  he 
  has 
  adviced 
  and 
  

   assisted 
  me, 
  and 
  for 
  which 
  I 
  can 
  never 
  thank 
  him 
  enousjh. 
  

  

  Concerning 
  the 
  mode 
  of 
  growth 
  of 
  the 
  diatoms, 
  it 
  seems 
  

   probable 
  that 
  generally 
  they 
  do 
  not 
  live 
  at 
  a 
  greater 
  depth. 
  

   In 
  enormous 
  masses 
  they 
  occur 
  fixed 
  to 
  stones, 
  seaweed, 
  and 
  

   smaller 
  algae, 
  and 
  to 
  the 
  very 
  bottom 
  in 
  the 
  waterline 
  and 
  

   at 
  a 
  depth 
  of 
  a 
  few 
  inches. 
  Towards 
  the 
  deeper 
  water 
  they 
  

   increase 
  very 
  suddenly 
  in 
  number, 
  so 
  that 
  at 
  a 
  depth 
  of 
  only 
  a 
  

   few 
  fathoms 
  the 
  bottomsoil 
  specimens 
  very 
  seldom 
  contained 
  

   any 
  living 
  frustules, 
  and 
  in 
  the 
  mud 
  from 
  greater 
  depths 
  the 
  

   valves 
  found 
  imbedded 
  are 
  always 
  very 
  scarce. 
  So 
  for 
  in- 
  

   stance 
  on 
  the 
  coast 
  near 
  Helsingfors 
  in 
  a 
  great 
  many 
  samples 
  

   taken 
  up 
  from 
  the 
  bottom, 
  I 
  always 
  found 
  masses 
  of 
  diatoms 
  

   in 
  the 
  shallow 
  bays, 
  — 
  1 
  — 
  2 
  feet 
  deep, 
  — 
  but 
  almost 
  no 
  

   valves 
  or 
  whole 
  frustules, 
  and 
  not 
  any 
  living 
  diatoms 
  at 
  all, 
  at 
  

   a 
  depth 
  of 
  2 
  fathoms 
  or 
  more. 
  The 
  few 
  species 
  that 
  I 
  have 
  

   found 
  imbedded 
  in 
  the 
  bottomclay 
  or 
  mud 
  from 
  the 
  deep 
  

   water, 
  generally 
  are 
  such 
  as 
  live 
  free, 
  — 
  not 
  fixed 
  — 
  , 
  

   swimming 
  in 
  the 
  upper 
  layers 
  of 
  the 
  water, 
  and 
  these 
  I 
  think 
  

   in 
  sunshine 
  and 
  fine 
  weather 
  live 
  floating 
  at 
  the 
  very 
  surface 
  

   of 
  the 
  water, 
  else 
  some 
  feet 
  underneath, 
  but 
  do 
  not 
  sink 
  down 
  

   to 
  the 
  bottom 
  till 
  after 
  death. 
  The 
  species 
  which 
  commonly 
  

   occur 
  in 
  bottom 
  specimens 
  are 
  : 
  Navicula 
  didyma 
  K, 
  N. 
  Smithii 
  

   Beéb., 
  N. 
  interrupta 
  K., 
  Pleurosigma 
  elongatum 
  Sm., 
  Coscino- 
  

   discus 
  polyacanthos 
  v. 
  balticus 
  Geun., 
  fragments 
  of 
  Coscin. 
  

   Oculus 
  Iridis 
  Ehb. 
  or 
  radiatus 
  Ehb. 
  On 
  the 
  contrary, 
  one 
  

   generally 
  misses 
  those 
  species, 
  which 
  in 
  such 
  enormous 
  

   masses 
  cover 
  the 
  bottom 
  and 
  the 
  seaweed 
  at 
  the 
  shore, 
  such 
  

   as 
  Melosira 
  Jurgensii 
  K., 
  M. 
  nummuloides 
  Dillw., 
  Bpithemiae, 
  

   Amphorae, 
  Cocconeis 
  Scutellum 
  E. 
  and 
  Placentula 
  E., 
  Gompho- 
  

   nema 
  balticum 
  Cl., 
  Achnanthes 
  longipes 
  Lgb., 
  Khoicosphenia 
  

  

  