WISCONSIN PETTOPLANKTON 93 



noid in the posterior region. Cells with two contractile vacuoles at 

 the base of the cilia and with a disciform eyespot in the upper third 

 of the cell. (Tychoplanktont). 

 Cells 9-16 IL broad, 12-20 /t long. 



Crawling Stone (rrr). 



CABTERIA KLEBSII (Dangeard) Dill. PI. 16, Figs. 2-4. 



Jahrb. f. wiss. Bot. 28: 353. 1895; Printz, Skr. Vidensk.-Selsk. Kristiana, Mat.- 

 Naturv. Kl. 1913 1 : No. 6: 13. 1914. 



Pithiscus Klebsii Dangeard, Ann. Sci. Nat. 7 Ser. Bot. 7: 137, pi. 12, figs. 

 1-6. 1888. 



Cells solitary, ellipsoid to ellipsoid-cylindrical, with a more or less 

 prominent beak at the anterior end. Chloroplast cup-shaped, massive, 

 with a large pyrenoid at the posterior end. Cells without an eye-spot 

 and with two contractile vacuoles at the base of the cilia. Cilia about 

 twice as long as the cells. Palmella stages containing many cells at 

 times. (Tychoplanktont). 



Cells 5-10 /i broad, 8-16 p long. 



Pokegama (1) (r). 



Family VOLVOCACEAE. 



Cells always motile and in coenobia of definite shape that contain a 

 definite or an indefinite number of cells. Colonies enclosed in a homo- 

 geneous, hyaline, gelatinous envelope. Cells of colony all alike or dif- 

 ferentiated into vegetative and reproductive cells. Vegetative cells 

 spherical, ellipsoid, pyrif orm or disciform ; with or without connecting 

 cytoplasmic processes; always biciliate. Chloroplasts generally cup- 

 shaped and containing one pyrenoid. Vegetative cells usually with an 

 eyespot and two contractile vacuoles. 



Asexual reproduction by the division of all or certain of the cells in 

 the colony to form autocolonies. 



Sexual reproduction by a division of all cells in the colony to form 

 isogamous zoogametes or heterogamous zoogametes of slightly different 

 size; or the formation of motile antherozoids from certain cells and 

 large immobile oospheres from others. Zygotes with smooth or sculp- 

 tured walls. 



