PROTOCOCCACE^:. 45 



Pediastrum rotula. (Ehr.) Br. Unwell. Alg. p. 101. 



Ccenobium orbicular or oblong, size and number of cells 

 variable, 4-8-16-32, pierced with openings, bright green, even ; 

 cells of the periphery truncate at the base, more or less dilated 

 upwards, deeply bifid, sinus acute, lobes straight, narrow, biden- 

 tate, teeth erect or divergent, somewhat bent ; cells of the 

 centre variable in form, usually polygonal, repand, or notched, 

 containing a single paler spot, sometimes not visible. 



Eabh. Alg. iii. p. 79. 



Pediastrum heptactis, Hassall Alg. t. 92, f. 9. 



Pediastrum incisum, Hassall Alg. t. 92, f. 8. 



In pools, &c., throughout Europe. 



Plate XVIII. fig. 2. b, marginal cell ; a, 4-celled ccenobiam ; c, 

 6-celled coenobium ; d, 8-celled coenobinm ; e,f, h, 16-celled coeaobium j 

 g, irregular ccBnobium. 



Sub-Family 8. SORASTEE^. 



Cells polygonal, often shortly horned, associated in a hollow, 

 sphaerical or cubical ccenobium ; cell-membrane thin ; cell- 

 contents green, homogeneous, then granular ; chlorophyllose 

 vesicle central or sublateral. Propagation by gonidia, in two 

 modes in the same species (simultaneous, or after division), 

 united into a coenobium within the mother-cell, escaping by 

 rupture of the membrane. Rabh. Alg. Eur. iii. 79. 



GENUS 30. CCE LA STRUM. Nag. (1819.) 



Coenobium globose, hollow within, formed of a single stratum 

 of cells, reticulately pierced. Rabh. Alg. Eur. iii. 79. 



Frond, or family, hollow, globular, or subcubical, composed of poly- 

 gonal or sphaerical cells, united in one layer into a hollow clafchrate net- 

 like family, the cells drawn out on the exterior into one or more lobes, 

 or simply sphasrical ; propagating by the segmentation of the cell-con- 

 tents into a definite number of portions which become arranged into a 

 hollow young frond, resembling the parent, ultimately set free by the 

 bursting of the parent cell. Pritch. 755. 



Ccelastrum sphaericum. Nag. Ein. Alg. 97. 



Coenobium globose or subglobose, composed of 4-8-16 or a 

 larger number of cells, perforated, areolse 3-4-5-6 angled ; cells 

 rounded, by mutual pressure angular, outer angles somewhat 

 conical, obtusely rounded at the apex ; interstices 5-6 angled. 



SIZE. Coenobium -04-'085 mm. diam. ; cells '021-'023 mm. 



Ccelastrum Naegelii, Rabh. Alg. iii. 79. Archer in Pritch. 

 Infus. p. 755, t. 1, f. 49-55. 



In boggy places. 



Plate XIX. fig. 2. a, h, families magnified 400 diameters ; c, cell 

 magnified 800 ; d, cell of C. cubicum, with two obtuse processes ; e, cell 

 of Ccslastrum, perhaps C. cambricum, with one obtuse process. 



H 



