On the Pithophor-ace^. 47 



the order would embrace only tropical (and subtropical) forms. At all 

 events it has the centre of its geographical distribution between the 

 tropics, and in this respect stands alone among the orders of freshwater 

 nlgaî as yet known. 



If we inquire in which parts of the world the different species of 

 Pithophoracece are met with, we find that four, viz. P. sumatrana (v. Mart.) 

 nob., P. polymorpha nob., P. Roettleri (Roth) nob. and P. Zelleri (v. 

 Mart.) nob. are found in Asia; that three, viz. P. œqualis nob., P. oedo- 

 (jonia (Mont.) nob. and P. Cleveana nob. are found in America; and 

 one, viz. P. kewensis n oh., in Europe. ') Even in Australia a PkJiophora 

 is found, the one mentioned before as existent in the Grunowian collec- 

 tion, gathered in the isles of Samoa. From Africa alone no Pithophoraceœ 

 are as yet known; but that they exist there is more than probable, 

 because everything we know of their distribution seems to indicate that 

 they are common in the freshwater pools of the tropical countries. — 

 As to a more particular account of the localities of the Pithophoraceœ 

 as yet known, I may refer to the descriptions of the different species 

 given hereafter. 



Vni. DESCRIPTION OF THE SPECIES. 



Before giving a description as complete as possible of the spe- 

 cies of Pithophoracece known to me, I will here try to give a diagnosis 

 of the order. 



ORDER PITHOPHORACECE nob. 



Chlorophyllif erous cladophora-like freshwater algge, con- 

 sisting of cells, formed by bipartition of the terminal cell. 

 The thallus having two distinct parts, viz. l:o the cauloïd part, 

 developed from the germinated spore upwards, propagative 

 and almost always branched; the branches placed a little 

 space below the top of their supporting cells; 2:o the (mor- 



') As to the country where P. keioensis nob. is indigenous, it seems 



probable that it is the tropical part of America. Here both the species occur, 



which show the nearest relationship to P. ];nvcn.sis nob., viz. P. oedogoma (Mont.) 

 nob. and P. Cleveana nob. 



