HYALOTHECA. 231 



ENGLAND. Cumberland ! and in the plankton of 

 Ennerdale and Derwent Water ! Westmoreland ! (at 

 2400 feet on Helvellyn) and in the plankton of Brother's 

 Water and of Codale, Easedale, and Eed Tarns. Lan- 

 cashire (Ralfs). W., N., and E. Yorks. Cheshire and 

 Leicester (Roy). Suffolk ! Essex ! Cambs ! Berks ! 

 Warwicks ! (Witts). Worcs ! Gloucester (Ralfs). 

 Surrey ! Sussex (Ralfs). Kent! Hants! Wilts! 



fc/ i/ / 



Devon ! (Harris). Cornwall ! 



WALES. Common ! (zygospores common and up to 

 2200 feet on Glyder Each, and at 2700 feet on Glyder 

 Fawr. 



SCOTLAND. General ! and in the plankton ! Wig- 

 town (with zygospores) ! Lewis and Harris, Outer 

 Hebrides ! Orkneys and Shetlands ! 



/ 



Common ! Zygospores abundant ! In the 



plankton. Mayo !. Galway and Kerry ! 



Geogr. Distribution.- France. Germany. Switzerland. 

 Austria. Hungary. Roumania. Turkey. Italy. Por- 

 tugal. Norway. Finmark. Sweden. Denmark. Born- 

 holm. Finland. Poland. X., S.. and Central Russia. 

 Faeroes. Xova Zembla. Spitzbergen. Greenland. 

 Siberia. Central China. India. Ceylon. Burma. Siam. 

 Singapore. Java. Australia. E. and Central Africa. 

 Azores. United States. X. W. Canada. W. Indies. 

 Guiana, Colombia. Brazil. Paraguay. Argentine. 



/ 



H. dissilicns is one of the most ubiquitous of Desmids, and 

 often occurs in great abundance. It is generally distributed in 

 bogs and ditches, is not infrequent in plankton, and is often 

 found conjugated. The zygospores also occur as a rule in great 

 numbers. The broad gelatinous sheath which is almost invari- 

 ably present is secreted by special pores in the cell-wall, which 

 are crowded together in a broad band on the lateral walls of 

 each semicell. The external aperture of these pores is often 

 closed by a hardened gelatinous structure which renders them 

 conspicuous, so that the wall appears to be punctate or finely 

 granulate. This punctate appearance has been noted by several 

 observers, but it is only due to phenomenon of jelly-secretion. 

 The end cell of the filament has its free end also covered with 



