Uenmark has hitherto been the most northerly country 

 from which fairly detailed reports of the fresh-water Bryozoa 

 have appeared. From Daly el Is' (1848 p. 87) and Allmans' 

 researches (1856 p. 78) we know that CHstatella mucedo and 

 Plumatella fungosa occur in Scotland, and that P. repens has 

 probably a wide distribution in that country. As regards Norway 

 Kraepelin only reports (1887 p. 99) that he has taken Ра/ггс?г- 

 cella in the neighbourhood of Kongsberg and Plumatella fruticosa 

 (1887 p. 120) near Drammen. To my knowledge we have hardly any 

 reports at all from Sweden whereas a good many from Finland. 

 From Nurmijärwisö ca. 6 miles to the north of Helsingfors 

 Paludicella, Fredericella, Plumatella princeps, var. fruticosa, 

 P. polymorpha var. repens and cœspitosa besides Cristatella 

 have been reported by Stenroos (1898 p. 50). As far as I am 

 aware no growing Bryozoa have been found farther north. ' From 

 the existing evidence as to the boundaries of the fresh-water 

 Bryozoa it would seem that they do not extend very far to the 

 north; their geograflcal distribution would seem to justify our con- 

 sidering them as organisms requiring a considerably high summer 

 temperature to enable them to thrive. Yet several circumstances 

 make it questionable whether this opinion will hold good. 



In the first place it has been proved that fresh-water Bryozoa 

 occur at considerable depths where the annual temperature is 

 but low. Du Pie s si s thus pointed out a species of Frede- 

 ricella, by Forel termed F. Du Plessisi (1901 p. 113). It is 

 common in the upper part of the abyssal region at ca. 45 m. 

 where Forel obtained ca. 150 specimens at a single dredging. 



5* 



