WISCONSIN PHYTOPLANKTON 125 



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Sub-family MICE ACT 'INIEAE. 



Cells solitary or in colonies; spherical or ovoid; with long hyaline 

 setae or spines completely covering or restricted to certain parts of the 

 cell wall. Chloroplast single and cup-shaped ; or laminate to disciform 

 and from one to several in each cell. Chloroplasts generally with pyre- 

 noids. 



KEY TO THE GENERA. 

 Cells spherical. 



Cells organized into definite colonies MICRACTINIUM (p. p.) 



Cells solitary. 



Wall covered with fine hair-like setae. 



Setae thickened in lower third ACANTHOSPHEAERA 



Setae not thickened in lower third GOLENKINIA 



Wall covered with delicately tapering spines ECHINOSPHAEKEIXA 



Cells ovoid. 



Cells organized into definite colonies MICRACTINIUM: (p. p.) 



Cells solitary. 



Setae somewhat tapering LAGERHEIMIA 



Setae not tapering FRANCEIA 



MICRACTINIUM Fresenius 1858. 



Cells spherical or ovoid, in colonies of 4-32 or more, generally quad- 

 rately arranged in one plane but sometimes tetrahedrically disposed. 

 Cell wall delicate, with 1-7 long hyaline setae that are not thickened 

 at the base lying on the free surface of the cells. Chloroplast single, 

 parietal, cup-shaped ; with one pyrenoid. 



Reproduction by the division of contents of any cell to form a 4- or 

 8-celled autocolony, the young colony being liberated by a rupture of 

 the mother cell wall into four parts. Young coenobia frequently re- 

 maining attached to the parent coenobe for some time. 



KEY TO THE SPECIES. 



Cells spherical M. PUSILLUM 



Cells ovoid M. QUADEISPINUM 



MICRACTINIUM PUSILLUM Fresenius. PI. 28, Figs. 1-3. 



Abh. Senckenb. Naturf. Ges. 2: 236, pi. 11, figs. 46-49. 1858; G. M. Smith, Bull. 

 Torr. Dot. Cl. 43: 477, pi. 25, fig. 18. 1916. 



Richteriella ~botryoides (Schmidle) Lemmermann, Hedwigia 37: 307, pi. 10, 

 figs. 1-6. 1898. 



Richteriella botryoides forma fcnestrata Chodat, Mater, pour la flore crypt. 

 Suisse I 3 : 194, fig. 110. 1902. 



