center, the entire colony invested by a wide, hyaline, gelatinous 

 envelope; cells with 1 or 2 parietal chloroplasts, each with a pyrenoid. 



Key to the Species 



Cells ellipsoidal or ovoid; colony ovoid D. Ehrenbergianum 



Cells spherical; colony usually globose D. pulchellum 



Dictyosphaerium Ehrenbergianum Naegeli 1849, p. 73 



PI. 51, Figs. 3, 4 

 Colony ovoid, composed of 8-30 ellipsoidal cells with 1 or 2 

 parietal or cup-like chloroplasts, cells attached in groups of 2 or 4 

 at the ends of fine, branched strands; cells 4-6/x in diameter, 8-10/i, 

 long. 



Common in the plankton of many soft water lakes. Mich., Wis. 



Dictyosphaerium pulchellum Wood 1874, p. 84 

 PI. 51, Figs. 5-7 



Colony spherical or ovoid, composed of as many as 32 spherical 

 cells arranged in series of 4 on dichotomously branched threads, 

 inclosed in mucilage; cells 3-10^ in diameter. 



This species is sometimes a conspicuous component of the 

 plankton in acid bog lakes. Taylor (1935) has found it in the leaves 

 of pitcher plants ( Sarracenia purpurea L. ) 



Generally distributed in many soft water as well as semi-hard 

 water lakes. Mich., Wis. 



TROCHISCIA Kuetzing 1833b, p. 592 

 Free-floating (or sometimes subaerial), spherical, unicellular 

 plants with thick walls which are either smooth or variously 

 sculptured and decorated (reticulations, warts, spines); with 1 to 

 several plate-like, parietal chloroplasts; pyrenoids 1 or more. 



Some care must be used in distinguishing members of this genus 

 from the zygospores of some desmids. The latter have a single, 

 massive chlorophyll-bearing body of indefinite form. 



Key to the Species 



1. Wall decorated with granular, wart-Uke or spine-like roughenings 2 



1. Wall decorated with ridges which may be concentric 



and parallel, or may form a reticulvim 3 



2. Granulations sharply pointed and numerous T. aspera 



2. Granulations low and blunt, not so closely 



arranged as above T. granulata 



3. Wall with concentric ridges which form 



low, blunt protuberances T. obtusa 



3. Wall with reticulate ridges 4 



4. Reticulations coarse, forming '8-10 visible polygonal areas T. Zachariasii 



4. Reticulations fine, forming as many as 35 



visible areas on the wall T. reticularis 



[ 238 ] 



