170 FKESH-WATER ALG^J OF THE UNITED STATES. 



could be arranged within the compass of a single mesh of 

 an older plant. 



Often very abundant in sluggish, and stagnant waters. 

 Plate CLIV, figs. 11-14, parts of coenobia of various de- 

 grees of development ; figs. 15, 16, very young coenobia ; 

 fig. 17, cell with microgonidia ; fig. 18, cell with macro-' 

 gonidia; fig. 19, free n^icrogonidia ; fig. 20, active macro- 

 gonidia or zoospores. The latter four are taken from Colin. 



Genus 42, COELASTEUM, Naeg. 



Coenobium globose, hollow within, formed of a single stratum 

 of green cells, primarily globose ; later the coenobium appears 

 reticularly pierced; in older growths the cells are sometimes 

 polygonal from mutual pressure on the sides. 



Macrozoospores develop daughter coenobia within the ma- 

 ternal cell, which escape by the rupture of the membrane of 

 the latter. 



COELASTRUM MICROPORUM, 



Coenobium spherical, diameter, 40-100 //, consisting of 

 eight, sixteen or thirty-two globose cells, with interstitial 

 openings through which the interior of the coenobium may 

 be penetrated. Diameter of the globose cells varies accord- 

 ing to age ; sometimes as much as 25 yw. 



Var. SPECIOSUM, Wolle. 



A large and beautiful variety in which the green spherical 

 cells appear to be joined in the center of the coenobium 

 by gelatinous cords. Diameter of cells and of coenobium 

 rather larger than the type-form. 



This beautiful form may be a distinct species, but have 

 hitherto seen too few perfect specimens to pronounce it such. 

 Ponds and pools. 



Plate CLYI, figs. 1-3, a fully developed form and two 

 younger specimens ; fig. 4, var. speciosum. 



COELASTRUM CAMBRICUM, Arch. 



Coenobium spherical ; cells angular, rounded on the 

 exterior margin, each bearing a single truncate tubercular 

 process ; sometimes with, but often without interstices. 



The only description of this species at my command is 

 very brief and without illustration. I infer my plant is the 

 same and hence adopt the name provisionally. The plant 

 is entirely unlike C. sphaericum and C. cubicum, Naeg. 



