Rivulariacex 



45 



form an expanded stratum on wet rocks and submerged stones (tig. 35). In Rimdaria the 

 filaments are disposed to form subglobose or hemispherical, attached masses, sometimes 





Fig. 34. A and B, Stigonema miniitum, Hass. ; A, x 100; B, x 440. C fi, St. oceUatum 

 (Dillw.)' Thur. ; C, xlOO; D &m\ E, x 400. ft, heterocyst. 



Fig. 35. A and B, Calothri.r ixirh'tina (Nag.) Thur. (7, Dichotlirix intcrrupta W. & 

 G. S. West. D, D. Orsiniana (Kiitz.) Born. & Flah. All x 420. 



gelatinous and sometimes incrusted with lime. In Glceotrichia, which occurs largely in 

 the plankton, the gelatinous mass is usually free-floating. The genus scarcely differs from 

 Ri.vularia, except in the formation of large cylindrical resti tig-spores. In Honweotln-i.>- 

 and two other genera there are no heterocysts. 



