32 COCCOPHYCF^E. 



Folyedrium tetraedsricum. Nag. Einz. Alg. 



Cells regularly tetrahedrical ; angles obtuse, mucronate. 

 SIZE. Cells -015--03 mm. diam. 



Eabh. Alg.iii. 62. Archer, Micr. Journ., 1866, p. 62. 

 In pools. 



This might possibly be mistaken for the end view of some species of 

 Staurastrum, against which error it is essential that beginners should be 

 cautioned. 



Plate X11I. fig. 3. Cells magnified 400 diameters. 



B. Angles radiato-elongated. 

 Folyedrium longispinum. (Perty.) Rabk. Alg. in., 62. 



Quadri-radiate, radii thin, elongated, scarcely thickened into 

 a body in the centre. 



SIZE. Length of arms '03--05 mm. 



Phycastrum longispinum, Perty Kl. Lebensf. t. xvi., f. 30. 



In pools. N. Wales (A. W. Wills). 



A peculiar species, which at first sight seems to have but little re- 

 lationship with the other species figured. It is often found associated 

 with Desmids, and delights in similar localities. 



Plate X11I. fig. 2. a, b, c, d, cells magnified 400 diameters. 



C. Angles lobed. 

 Folyedrium enorme. (Ralfs.) Rabli. Alg. in., 63. 



Cells irregularly tetrahedrical, with the angles produced, 

 hyaline, deeply bilobate ; sometimes repeatedly bilobed, with the 

 lobes mucronate. 



SIZE. Cells '025-'04 mm. diam. 



Staurastrum enorme, Ralfs, t. 33, f. 11. 



In pools. 



" Frond very irregular and variable in form. Sometimes the front 

 view differs but little from the end one. Usually, however, there is a 

 slight constriction at the junction of the segments, but I have never ob- 

 served any difference in the endochrome at that part. The spines, which 

 are almost confined to the angles, are irregular, some simple and some 

 branched. The end view has three or four broad and very irregular 

 lobes ; these are spinous and more or less emarginate, and frequently 

 one lobe is much broader and more spinous than the others. The spines 

 on each lobe form two groups, separated by the notch ; they vary much 

 in size, and are either simple and subulate, or else forked ; sometimes 

 the forked spines are again divided at the apex." Ralfs. 



A very variable plant, formerly included with the Desmidiea?, but 

 separated on account of its different mode of propagation. 



Plate X1I1. fig. 4. Cells magnified 400 diameters. Lateral and end 

 views. 



Sub-Family 4. SCENEDESME^. 



Cells elliptic, oblong, or cylindrical ; cell-membrane very thin ; 

 cell- contents at first homogeneous, afterwards granular ; chloro- 

 phyllose vesicle central or siiblateral, and often a lateral colour- 

 less spot; cells 2-4-16, cither joined in a single series or forming 



