218 ChlorophycecB 



fragile character, the cells in some instances being held in position 

 only by the enveloping mucus. There is a single chloroplast in 

 each cell, which may contain one or several pyrenoids or may be 

 destitute of them. In rare instances the chloroplast is fragmented. 

 The cell-wall is firm but delicate. 



Multiplication is principally by autospores and autocolonies, 

 and this often takes place by the oblique division of the contents 

 of the mother-cell. 



The following genera of the Selenastrese are British : 



A. Cells or colonies almost destitute of mucus. 



* Cells attenuated to acute apices ; multiplication by 

 oblique division of contents of mother-cell, the 

 daughter-cells often remaining loosely attached 

 by their apices Dactylococcus. 



** Cells ellipsoid or much attenuated, forming more 

 or less definite colonies consisting of a row of 

 cells in one plane Scenedesmus. 



*** Cells sublimate or ellipsoid, arranged in groups 

 of four in one plane, the groups being attached 

 to form an irregular colony Dimarphococcus. 



**** Cells elongate and acutely attenuated, often 

 lunate, solitary or loosely grouped in irregular 

 bundles. 

 + Cells of moderate length, usually with not more 



than one pyrenoid Ankistrodesmus. 



ft Cells greatly elongated, pyrenoids numerous... Closteriopsis. 



***** Cells ovoid, oblong, or club-shaped, often at- 

 tached by their apices to form radiating colonies Actinastrum. 



****** ( i e ii, s attenuated, lunate, arranged back to 



back to form definite colonies Selenastrum. 



B. Colonies enveloped in a copious mucus. 



Cells lunate or much curved, disposed more or less 



irregularly in the enveloping jelly Kirchneriella. 



Genus Dactylococcus Nag., 1849. [Indus. Coccomyxa, 

 Schmidle, 1901.] The cells are ellipsoidal, fusiform or pyriform, 

 often sublimate and generally with acute apices, which are some- 

 times unequally prolonged into spine-like processes. They occu' 

 solitary or loosely connected by their acute extremities to fori 

 fragile colonies of few cells. The chloroplast is single and pariet; 

 and sometimes contains a single pyrenoid ; occasionally it becomes 

 fragmented into two, three, or four parietal pieces. Some species 

 are truly aquatic, but most of them occur on wet rocks and moist 

 surfaces, forming a dark green mucous stratum. Multiplication is 



