Chtftopelt idea 181 



Reproduction has been observed to take place in several of the 

 genera by zoogonidia with two or four cilia, and by biciliated 

 isogamous gametes. 



Throughout the entire family there is a marked dorsiventrality 

 such as appears elsewhere in the Coleocha3tacea3, Trentepohliaceae, 

 etc. 



The following British genera are known : 



A. Plants with a disciform thallus furnished with 



scattered bristles Chietopeltis. 



B. Plants consisting of a loose aggregate of cells in one stratum. 

 * Each cell with one seta or bristle. 



Bristles with a basal sheath ; chloroplasts 



parietal Ckoetosphceridium. 



** Each cell with several setce or bristles. 



t Bristles few, with basal sheaths Conochcete. 



tt Bristles many, without basal sheaths Polychcetophora. 



Genus Chsetopeltis Berth., 1878. The thallus is a flat plate, 

 almost circular in outline, and consists of a single layer of compact 

 cells, more or less radiating from the centre. The growth of the 

 thallus is peripheral as in Goleochcete, but the cell-walls are much 

 more gelatinous. From the upper surface of the thallus a number 

 of scattered mucous seta? arise, which are unseptate, simple, and 

 of considerable length. Each cell contains one parietal chloroplast, 

 which is often much lobed and perforated, and is furnished with a 

 single pyrenoid. Reproduction takes place by zoogonidia of which 

 2 8 arise from a mother-cell, each one possessing four cilia. 

 Isogamous gametes are also produced, similar in appearance to the 

 zoogonidia but with two cilia. 



Ch. orbicularrs Berth, is not an uncommon plant in this country, occurring 

 as an epiphyte on the stems and leaves of various aquatic Phanerogams. The 

 thallus varies greatly in size and sometimes reaches a diameter of 1 mm. 



Genus Chsetosphseridium Klebahn, 1892 1 . The cells are 

 small and spherical, generally occurring in loose aggregates, 

 epiphytic on larger Alg* and other aquatic plants. They are 

 sometimes enveloped in mucus, but more often quite destitute of 

 a gelatinous investment. Klebahn states that the cells are com- 

 monly joined in a short filament by means of empty cylindrical 

 utricles, but I have not observed the presence of these structures 



1 Klebahu in Jahrbiich. wissensch. Bot. xxiv, 1892, pp. 268282, pi. 4. 



