Confer void Alg(je. 
53 
The vesicle sometimes presents delicate ciliary processes on 
the outside. The zoospores have two cilia, according to 
Al. Braun.* They have no ' eye-spot.' 
Clathrocystis ^ruginosa. 
Clathrocystis, Nov. Gen, Frond a microscopic gelatinous 
body, at first solid, then saccate, ultimately clathrate, (frag- 
ments of the broken fronds occurring in irregularly-lobed 
forms,) composed of a colourless matrix, in which are im- 
bedded innumerable minute gonidia, which multiply by divi- 
sion within the frond as it increases in size. (No zoospores or 
resting-spores observed.) 
C. (Bruginosa. (PI. IV., figs. 28 — 36.) Fronds floating in 
vast strata upon fresh-water pools, forming a bright green 
scum, presenting to the naked eye a finely granular appear- 
ance ; when dried appearing like a crust of verdigris. Gonidia 
or green cells, with a distinct membrane, about 1-8000" in 
diameter, leaving a hyaline border at the surface of the fronds ; 
full-grown fronds, 1-50" to 15'' in diameter. Microhaloa ceru- 
ginosa, Kiitzing. (' Linnaea,' viii, p. 371, PI. 8, fig. 23.) 
Microcystis icthyohlahe^ Kiitz., ^ Phyc. Gen.' ex parte. Mene- 
ghini, ' Monogr. Nostoch.' p. ].04. Microcystis ceruginosa, 
' Tab. Phyc' i., Tab. 8. Polycystis (Bruginosa, Kiitz., ' Sp. 
Alg.,' p. 210. " Flos Aquoi^'^ ' Treviranus,' Linnaea, xvii., 
p. 51, PI. 3. On fresh-water lakes. 
This remarkable form does not appear to have been ob- 
served hitherto in Britain. We found it in the autumn of 
1855, forming a scum extending over a large portion of the 
surface of the lake in the Royal Botanic Gardens at Kew. 
A portion of it, brought home and preserved in a room in a 
bottle of water, continued to grow healthily until the middle 
of winter. 
It is very well described in the paper of Treviranus above 
referred to ; but none of Kiitzing's descriptions mention its 
remarkable mode of growth or its peculiar form when perfect. 
Apparently that author has only seen it in a dry state ; it 
does not agree with the definitions of the genera Microcystis 
or Microhaloa ; and as the name Polycystis has been occupied 
in the Fungi, we have ventured to add to the already confusing 
synonymy, by giving it a distinctive and characteristic name. 
The smallest fronds met with are usually roundish or ellip- 
soidal, of the character shown in PI. IV., figs. 28 and 34. 
When quite young they appear to be solid, but as they grow 
by the multiplication of the internal gonidia, and the secretion 
of gelatinous matter, the expansion takes place chiefly near the 
* ' Verjungung,' &c., Eay Soc. Vol. 1853, p. 209. 
/2 
