Semi-Centenuial Volume. 161 



11. Cells free or united in g:elatinous colonies, uninucleate, of definite 

 form, with sinpfle chromatophore. 



* Cells dividing vegetatively II. Scendesvnacex. 



* * Vegetative cell -division rare and abnormal. 



I. Protococcaceie. 



Family I. Protococcaceie. 



1. Characium. 



Cells solitary, often distinctly stipitate. 



Key to the Species of Characium. 



I. Sessile upon plants, cells 7-9 mic. in diam C. sessile. 



II. Cells erect, at first lanceolate, later ellipsoid, obtuse, 20-42 by 7-18 

 mic, stipe slender about 4 mic. long C. Niegelii. 



67. C. sessile Hermann. 

 Kansas: Horton, June, 1916. 



68. C. Na^gelii A. Braun. Plate III, fig. 20. 

 Kansas: Leavenworth, July, 1916. 

 Iowa (4); Nebraska (24). 



Family II. Scenedesmace^. 

 Key to genera of Scenedesmacese. 



A. Plants not living in cell of animals; no external gelatinous 

 thallus. 



* Mature cell solitary, mother cell elongate, acinular or fusi- 

 form, dividing by oblique walls into daughter cells. 



1. Rhaphidium. 



* * Mature cells united in colonies. 



a. Cells elongate, side by side in a single or double series. 



2. Scenedesmus . 

 h. Cells without spinous projections, symmetrically ar- 

 ranged about a center, united to the center by gelatinous 

 strands. 



Strands unbranched, short 3. Coelastriini . 



Strands unbranched, spherical cells at end. 



4. Dictyosphaerinm. 

 1. Rhaphidium (Ankistrodesmus) . 



Kpij to Species. 



I. Cells 12-25 diam. long, ends very acute R. falcutum. 



II. Cells 3-12 diam. long, ends apiculate, cells variously twisted and 

 curved R. convolutum. 



69. R. falcatum (Corda) Cooke. {R. polymorphum Wolle, 

 Ankistrodesmus falcatus (Corda) Ralfs.) 



Kansas: Paola, March, 1916; November, 1915; Cha- 

 nute, November, 1915; Leavenworth, November, 

 1915; Ottawa, November, 1915. 



Iowa (4); Missouri (11); Colorado (15); Nebraska 

 (25). 



70. R. polymorphum var. contortum. (Thur.) Wolle (A. 

 falcatus var. spiralis (Thur.) West.) 



Kansas: Lyndon, March, 1916; November, 1915; Oc- 

 tober, 1916. 

 Missouri (11). 



71. R. polymorphum. var. sigmoideuvi Rab. Plate III, 

 fig. 22. 



Kansas: Burlington, April, 1916; Independence, 

 March, 1916, December, 1915; Lyndon, March. 1916; 

 Jewell City, October, 1916. 



Nebraska (24). 



1 1- Acad. 8ci. — 2199. 



