212 CYSTIPHOR.E. 



XVXicrocystis protogenita. (Bias.) Eabli. Alg. Eur. n., 51. 



Thallus membranaceous, thin, green; families small, angular 

 from mutual pressure ; cells small, spherical ; cell-contents 

 granular, pale blue-green. 



SIZE. Families, -02 mm. Cells, -0015--002 mm. 



Micraloa protogenita, Bias. Alg. Micr. t. xix. Meneg. Nost. 

 t. xiv., fig. 1 (partly). 



In water long standing, stagnant ditches, amongst other 

 Alga3, &c. 



Plate LXXXVI. fig. 5. Families magnified 400 diam. 



XKicrocystis marginata. (Meneg?) Kirch. Alg. Schl. 255. 



Thallus spha3rical, flattened, or orbicular and lens-shaped, 

 sometimes confluent, pale-green, colourless at the margin ; cells 

 minute ; cell contents blue-green, at length granular. 



SIZE. Cells -003--004 mm. Families 'S--03 mm. 



Anacystis marginata, Meneg. Nost. 93, t, 13, f. 1 , Kabh. Alg. 

 Eur. ii., 52. 



In ditches, free swimming. 



Plate LXXXVI, fig. 6. Families magnified 400 diam. 



GENUS 85. CLATHROCYSTIS. Henfrey. (1856.) 



Frond, a microscopic gelatinous body, at first solid, then 

 saccate, ultimately clathrate (fragments of the broken fronds 

 occurring in irregularly lobed forms) composed of a colourless 

 matrix, in which are imbedded innumerable minute cells, which 

 multiply by division within the frond as it increases in size. 

 Quart. Journ. Micr. Sci., 1856, p. 53. 



Clathrocystis aesruginosa. Henf. Micr. Journ. 1856, p. 53, f. 4, 



f. 28-36. 



Fronds floating in vast strata on freshwater pools, forming a 

 bright green scum, presenting to the naked eye a finely granular 

 appearance ; when dried, appearing like a crust of verdigris ; 

 cells minute. 



SIZE. Fronds -03--13 mm. ; cells '0025--0035 mm. 



Kabh. Alg. Eur. ii., 54. Kirch. Alg. Schles. 254. 



Microcystis ceruginosa, Kutz. Tab. i., t. 8. 



Polycystis ceruginosa, Kutz. Spec. 210. 



On fresh water lakes. 



"The smallest fronds met with are usually roundish or ellipsoidal. 

 When quite young they appear to be solid, but as they grow by the multi- 

 plication of the internal cells and the secretion of gelatinous matter, the 

 expansion takes place chiefly near the periphery, so that the frond becomes 

 a hollow body. The walls of the sac then give way, and, as the expan- 



