﻿12 
  JUHLIN-DANNFELT, 
  ON 
  THE 
  DIATOMS 
  OF 
  THE 
  BALTIC 
  SEA. 
  

  

  of 
  the 
  water, 
  a 
  very 
  great 
  influcnce 
  on 
  the 
  diatomaceous 
  

   vegetation. 
  

  

  Besides 
  these 
  marine 
  forms 
  which 
  occur 
  ratlier 
  com- 
  

   monly, 
  there 
  are 
  some, 
  whicli 
  I 
  almost 
  ne 
  ver 
  observed 
  living, 
  

   but 
  wliicb 
  are 
  very 
  often 
  found 
  in 
  the 
  bottomclay, 
  and 
  al- 
  

   ways 
  abundantly 
  occur 
  in 
  the 
  bathingsilt 
  from 
  Norrtelje, 
  

   Furusund, 
  Dalarö 
  and 
  Konneby, 
  as 
  well 
  as 
  in 
  some 
  recent 
  

   earths 
  of 
  eastern 
  Upland, 
  viz: 
  the 
  bottomsilt 
  of 
  the 
  peat- 
  

   mosses, 
  the 
  mud 
  from 
  the 
  bottom 
  of 
  some 
  lakes 
  in 
  the 
  same 
  

   region 
  and 
  in 
  the 
  silty 
  clay 
  that 
  sometimes 
  forms 
  the 
  soil 
  

   near 
  Norrtelje. 
  The 
  same 
  forms 
  also 
  occur 
  very 
  commonly 
  

   in 
  the 
  postglacial 
  clay 
  that, 
  from 
  its 
  colour, 
  is 
  called 
  black- 
  

   clay 
  (svartlera). 
  These 
  forms 
  are 
  Hyalodisciis 
  scoticus 
  (K.) 
  

   Geun., 
  Melosira 
  Westii 
  Sm., 
  M. 
  sulcata 
  Ehb., 
  Ehabdonema 
  

   arcuatum 
  K., 
  Rh. 
  minutum 
  K., 
  Coscinodiscus 
  Oculus 
  Iridis 
  

   E. 
  They 
  are 
  all 
  real 
  marine 
  species 
  which 
  still 
  occur 
  

   very 
  common 
  in 
  Kattegat 
  and 
  seem 
  to 
  have 
  been 
  very 
  com- 
  

   mon 
  in 
  the 
  Baltic, 
  when 
  it 
  was 
  in 
  more 
  open 
  corinection 
  

   with 
  the 
  Ocean 
  and 
  its 
  water 
  therefore 
  was 
  salter, 
  but 
  which 
  

   have 
  grown 
  less 
  frequent, 
  and 
  finally 
  almost 
  disappeared 
  as 
  

   the 
  water 
  has 
  becorae 
  less 
  salt. 
  

  

  Neither 
  as 
  living 
  nor 
  imbedded 
  in 
  mud 
  or 
  recent 
  earths 
  

   deposited 
  in 
  the 
  Baltic, 
  I 
  have 
  found 
  such 
  species 
  as 
  Acti- 
  

   noptychus 
  undulatus 
  K., 
  Coscinodiscus 
  excentricus 
  B., 
  C. 
  

   lineatus 
  E., 
  Syndendrium 
  Diadema 
  E., 
  Biddulphia 
  aurita 
  

   Lgb., 
  Rhabdonema 
  adriaticum 
  K., 
  Surirella 
  fastuosa 
  E., 
  Navi- 
  

   ciila 
  Lyra 
  E., 
  N. 
  fusca 
  Greg., 
  which 
  are 
  so 
  common 
  in 
  the 
  

   ocean, 
  and 
  also 
  in 
  the 
  Kattesat 
  characterize 
  the 
  diatomaceous 
  

   vegetation. 
  

  

  Generally, 
  when 
  a 
  marine 
  species 
  is 
  left 
  in 
  a 
  sea 
  the 
  

   water 
  of 
  which 
  is 
  gradually 
  growing 
  fresher^ 
  it 
  becomes 
  

   smaller 
  and 
  often 
  crippled. 
  The 
  marine 
  species 
  occurring 
  

   in 
  the 
  Baltic 
  scarcely 
  show 
  any 
  such 
  degeneration, 
  compared 
  

   with 
  the 
  same 
  species 
  living 
  in 
  salt 
  water, 
  except 
  that 
  gene- 
  

   rally 
  the 
  striation 
  is 
  a 
  little 
  denser 
  than 
  in 
  marine 
  specimens. 
  

   An 
  exception 
  makes 
  Melosira 
  Westii 
  Sm., 
  of 
  which 
  the 
  sub- 
  

   fossil 
  Baltic 
  form 
  is 
  much 
  smaller 
  than 
  that 
  one 
  from 
  the 
  

   marine 
  habitats; 
  the 
  Baltic 
  form 
  measures 
  about 
  0,01 
  mm. 
  

   in 
  diam., 
  the 
  marine, 
  0,02 
  — 
  0,04 
  mm. 
  Quite 
  the 
  contrary 
  is 
  

   the 
  case 
  with 
  Coscinod. 
  polyacanthos 
  Grtjn. 
  of 
  which 
  the 
  

   Baltic 
  form, 
  — 
  v. 
  baltica 
  Grun. 
  — 
  , 
  is 
  bis-o-er 
  than 
  the 
  form 
  

  

  