THE GREEN ALGAE OF NORTH AMERICA 173 



united by gelatinous filaments, is difficult to locate, and may 

 possibly belong in another genus. Nothing can be determined 

 until the plant is rediscovered. 



4. C. CAMBRICUM Archer, 1868, p. 65 ; ?Wolle, 1887, p. 170, 

 PI. CL/VI, fig. 5. Cells 6-12 p. diam., angular and somewhat 

 lobed, with a truncate projection at the middle ; interspaces 

 quite small ; colony 20-70 p. diam. Fig. 57. Mass. l^urope. 



5. C. RETICULATUM (Dangeard) Senn, 1899, p. 40, fig. r. 

 Cells 2-4-8-16, 6-24 fj, diam., connected with each other by more 

 or less numerous, arm-like prolongations of the membrane, 

 forming a basket-like network about the spherical or spheroidal 

 colony, which may continue intact for some time after the for- 

 mation of daughter cells in each cell of the colony. Lake Erie. 



Europe. 

 18. SORASTRUM Kiitzing, 1845, p. 144. 



Colonies unattached, solid, composed of 4-32 cordate, cune- 

 ate, reniform, or suboviform cells, which are united at the center 

 of the colony by short stipes, and radially arranged ; cells with 

 1-4 spines, projecting from the larger (exte/nal) end of each 

 cell ; chromatophore single, with one pyrenoid ; asexual repro- 

 duction by the colony breaking up into its individual cells, 

 which then, either at once or after division, develop each a new 

 colony, which bursts through the membrane. 



Differs from Coelastrum chiefly in the shape of the cells, and 

 in that the colony breaks up before the development of the new 

 colonies begins ; but the reproduction is not fully understood. 



KEY TO THE SPECIES OF SORASTRUM. 

 i. Outer angles of cells rounded, each with 2 spines. 



1. 5". spinulosuni. 

 i. Outer angles of cells ending each in a short, conical point. 



2. S. bidentatuin. 



1. S. SPINULOSUM Nageli, 1848, p. 99, PI. V.D ; Wolle, 

 1887, p. 171, PI. CL/VI, figs. 6-10. Colony 23-60 /u. diam.; cells 

 8-32, cuneate, outer end somewhat emarginate or subcordate, 

 and with two pairs of spines about 15 /x. long on each cell. Fig. 

 58. Me., Mass., Neb., Washington, Porto Rico. Europe. 



2. S. BIDENTATUM Reinsch, 1867, p. 86, PI. IV, fig. i. 

 Colony globose, about 30 ^ diam., of 8-16 cells, wedge-shaped, 

 elliptic in surface view, with a deep sinuate incision in the 

 outer edge, the angles slightly prolonged and somewhat acute. 

 Porto Rico. Europe. 



19. DICTYOSPHAERIUM Nageli, 1848, p. 72. 

 Cells originally spherical, with cup-shaped chromatophore 



