414 Dr. J. E. Gray on the Arrangement of the Families 



some fronds much the appearance of a Conferva (p. 177). 

 Dr. Hicks, from observing the same fact, seems to think that 

 Lynghya muralis, Schizogonium, and Prasiola are only states of 

 the same species. If this is the case, as the true Lynghya 

 have not been observed to change into any other plant, L. 

 muralis must be the young state of a plant putting on the form 

 of a genus of a different group (see Quart. Journ. Micros. Science, 

 July 1861). The development of Enteromorpha and of Ulva 

 clathrata have been described by Hassall (Brit. Freshwater Algse, 

 pp. 296, 304), and also by Greville in his ' British Algse.' 



Order 11. Macrospor^. 



The zoospores large, formed by the union of the endochrome 

 of two neighbouring cells in the same or contiguous threads, or 

 by the division of a single primary endochrome of a single cell. 



Suborder I. Trichomorpha. 



The plant formed of a thread-like series of cells. The pro- 

 pagation entirely, or at least chiefly, by zoospores. The endo- 

 chrome generally assumes some definite arrangement, often 

 forming one or more spirals or stars. 



Fam. 1. Zygnemaceae. 



Filaments free, floating, simple, articulated, thread-like, com- 

 posed of cylindrical seriated cells. Zoospores formed by the 

 union of the endochrome of two cells, simple. 



A. The zoospore formed by the union of the cells of two different threads. 



a. The conjugating filaments parallel, or nearly so, to each other. 



1. Zygnema. Endochrome in spiral lines; zoospore in the cells. 

 (Z. nitida, Hassall, t. 22. f. 1, 2.) 



2. Tyndaridea. Endochrome in two stellate masses; zoospore 

 in the cells. (7^. cruciata, Hassall, t. 38. f. 1.) 



b. The conjugating filaments angulated, bent, and coalescing at the bend. 



3. Mougeotia. [M. genufiexa, Hassall, t. 40. f. 2.) 



B. The zoospore formed by the union of the endochrome of the cells in 



the same thread. 



4. Rhynchonema. Endochrome in a spiral thread ; thread gene- 

 rally bent at an angle where the spore is formed. {R. ros- 

 tratum, Hassall, t. 33. f. 1.) 



Fam. 2. Thwaitesiese. 



Filaments free, floating, simple, articulated, thread-like, com- 

 posed of seriated cylindrical cells. The zoospore formed by the 



