12 p. T. CLEVE, SYNOPSIS OE THE NAVICULOID DIATOMS. 



strongly saline, and, in the latter case, whether the sea was tropical, temperate or arctic. There 

 are also reasons to believe that the accurate investigation of the geographical distribution of the 

 freshwater-forms will enable the geologist to ascertain the climate of the periods, when the fresh- 

 water deposits were formed. 



Considerations of that nature have induced me to pay much attention to the geographical 

 distribution of the Diatomacege. In the abundant literature upon the subject we find many lists 

 of diatoms ocurring in certain seas, countries, and deposits, but I have intentionally made very 

 little use of them, not being satisfied as to the accuracy of the determinations or limitations of 

 species by the various authors. I have besides had sad experience how easily one may be deceived 

 by slides of materials the loaclities of which are incorrectly named and which durnig the preparation 

 have not been kept rigorously isolated from other materials. For such reasons I have relied mainly 

 on my own observations only, though I still feel there may be among them some errors as to the 

 localities, arising from the latter cause, as I had no opportunity of controlling the mode in which 

 every slide, examined by me, had been prepared. 



Many diatoms are cosmopolitan, occurring in all parts of the world, but there are on the 

 other hand many species, genera and groups which occur only in certain seas and climates. The 

 arctic sea has its characteristic form of Triceratium arcticum (or Biddidphia Balcena), Campylodi- 

 seus Helianthus and others. There are numerous common atlantic species which have never been 

 found in the Arctic Sea. The tropical seas have their own peculiar species, not found in the At- 

 lantic or in the arctic sea. The same is the case with several freshwater-forms. Navicula {Dia- 

 desmis) confervacea, Achnanthes inflata, Cerataulus Icevis occur in tropical or subtropical countries 

 throughout the whole globe. Of Tahellaria flocculosa, one of the most frequent diatoms of Europe, 

 not a trace has been found either in South America from Ecuador to Argentina or in Australia 

 or New Zealand. Gomphonema geminatum, of frequent occurence in Scandinavia, Grt. Britain, and 

 the Alps, does not live in the main-land of Europe. The same is the case with Tetracydust 

 Diatomella JBalfoiiriana and others. Stauroneis Fulmen and St. Frauenfddiana are peculiar 

 to the Australian region. I could easily multiply these examples, but they are enough 

 to show that the study of the geographical distribution of the diatoms offers many points 

 of interest. 



I have examined a large number of samples of silurian clays and limestones, rhsetic and 

 cretaceous rocks of Sweden, but I never found in them a trace of a diatom. I have also searched 

 for diatoms in the eocene and oligocene strata of Paris, but hitherto in vain, though I think 

 it probable that they may yet be found there, as diatoms are found in the London clay of 

 Sheppey. On the other hand fossil diatoms are very frequent in strata of the tertiary period 

 in Barbados, Trinidad, New Zealand, Hungary, Japan, Denmark, etc. as is well known to every 

 diatomist. If it be true, as Pantocsbk believes, that the deposit of Kusnetzk belongs to the Trias, 

 this is the oldest known diatomiferous rock, as the statement by Castracane that diatoms occur in 

 the carboniferous system has never been verified. 



Some of the postglacial strata of Sweden are very rich in diatoms, and I have examined a 

 considerable number of them. Among them the glacial clay and glacial marl have constantly been 

 found by me free from diatoms, probably because the water, in which these deposits were formed, 

 was too turbid for their growth. The strata, formed later than these, usually contain diatoms of 

 both brackish and fresh-water habitat. The brackish-water-diatoms of the ancient baltic deposits 

 comprise forms occuring in the present time in the southern part of the Baltic, as Ehaidonema 

 arcuatum and Cosdnodiscus aster omphalus, both characteristic fossils of the Litorina-epoch. The 

 freshwater-species found in the Swedish post-glacial deposits are still living, but there are among 

 them several peculiar species, not hitherto found in the southern or median part of the country, as 

 Pinnularia cardinalis, Navicula amphihola, Nav. Semen, Anomoeoneis serians and others. Of 

 interest is the occurrence of Terpsinoe americana, now extinct in Europe (or at least in 

 northern Europe), in brackish or slightly brackish deposits of the Litorina-epoch. I have 



