128 WISCONSIN PHYTOPLANKTON 



Ireland. They were also dark colored and are more conspicuous than 

 in other members of the Micractineae. 



ACANTHOSPHAERA Lemmermann 1899. 



Cells spherical, solitary, with a single cup-shaped chloroplast con- 

 taining one pyrenoid. Cell wall thin, without a gelatinous sheath; 

 covered with many long hyaline setae that are thicker in the lower 

 third and then abruptly diminish to a very fine hair. 



Method of reproduction unknown. 



ACANTHOSPHAERA ZACHAEiASi Lemmermann. PI. 29, Figs. 6-8. 

 Forschungsbr. a. d. Biol. Stat. zu Plon 7: 118, pi. 1, figs. 10-11. 1899. 



Characters as those of the genus. (Euplanktont). 



Diam. cells (without setae) 9-14.5 /n; length setae 30-35 /*. 



Horse (rr). 



The chief distinction between this genus and Golenkinia is the thick- 

 ening of the lower part of the setae. 



Echinosphaerella gen. nov. 



Cells spherical, solitary. Cell wall thin, completely covered with 

 heavy, long, hyaline, delicately tapering and slightly concave, homo- 

 geneous spines. Chloroplast single, parietal, cup-shaped; with one 

 pyrenoid. 



Reproduction unknown. 



Echinosphaerella limnetica sp. nov. PI. 29, Figs. 9-11. 



Characters as described above. (Euplanktont). 

 Diam. cells (without spines) 9-12 /*. Spines 2.5-3 ^ broad at base, 

 20-25 v long. 



Horse (rr). 



The alga at once suggests a desmid zygospore, especially those of 

 certain Staurastrum species. In all desmid zygospores the chloroplast 

 is not definite and since the alga collected from Horse Lake has a 

 single, well defined, cup-shaped chloroplast with one pyrenoid the pre- 

 sumption is that it is a vegetative cell and not a zygospore. The 

 nearest genus is Echinosphaeridium Lemmermann where the setae 

 covering the wall have a broad tapering gelatinous sheath at the base. 

 In Echinospliaerella there is not a central hair-like seta with a gelati- 

 nous covering, but a homogeneous spine of considerable thickness at the 



