132 WISCONSIN PHYTOPLANKTON 



chloroplasts, presence of a vacuole, and cell division in one plane) are 

 ones which might be found in any Lagerheimia species. The setae, 

 however, are very delicate and do not taper so that the genus is pro- 

 visionally considered distinct from Lagerheimia. 



Sub-family SELENASTREAE. 



Cells elongate, straight or curved; with finely pointed ends or with 

 ends rounded. Solitary or associated in colonies containing an indefi- 

 nite number of cells. Colonies with or without a gelatinous envelope. 

 Cells generally with one parietal chloroplast that is with or without 

 pyrenoids. 



KEY TO THE GENERA. 

 Cells solitary. 



Ends of cells produced into setae SCHROEDERIA 



Ends of cells not produced into setae. 



Chloroplast with, an axial row of pyrenoids CLOSTEBIOPSIS 



Chloroplast never with more than a single pyrenoid . ANKISTBODESMUS (p. p. ) 

 Cells in colonies. 



Colonies not enclosed in a gelatinous sheath. 

 Cells straight, in loose fasiculate bundles or spirally 



twisted around one another ANKISTBODESMUS (p. p.) 



Cells curved, with convex faces towards one another SELENASTRUM 



Colonies enclosed in a gelatinous sheath. 



Cells curved KIBCHNERIELLA 



Cells straight. 



Colonies with cells in groups of two ELAKTOTHBIX 



Colonies with cells in groups of 2-4-8 QUADBIGETLA 



SELENASTRUM Reinsch 1867. 



Cells broadly to narrowly acicular, semilunar; joined by their con- 

 vex faces into colonies of 4-8-16 or more cells without a gelatinous en- 

 velope. Chloroplast single, parietal, laminate, on convex side of young 

 cells ; entirely filling older cells ; with one pyrenoid. 



Reproduction by any cell forming 2-4-8 autospores which, when 

 liberated, have the arrangement of the cells in an adult colony. Auto- 

 spores remaining attached to parent colony for some time. 



The statement is generally made that there are not more than six- 

 teen cells in a colony but I have found that in the plankton of Wiscon- 

 sin lakes the colonies sometimes contain over a hundred cells. 



